Tuesday, July 15, 2014

2014 Mid-Season Grades

Tonight is the All-Star game, which means we're at the halfway point in the season.  This is a good opportunity to evoluate how the Tiger players are performing and compare that to what was expected of them.


Avila has a 105 wRC+ and a 99 OPS+, which means that he's been a league average offensive player (100 is exactly league average).  The "+" is for his plus defense.  He ranks 4th among catchers in the defensive component of FanGraphs' version of WAR.  Avila has been a better player than some fans realize - for example, his 13.5% walk rate leads all Tiger hitters by a pretty wide margin.

Holaday has 22 hits in 79 at bats for a respectable .278 batting average.  However, 20 of those hits have been singles for a pathetic .038 ISO.  Unlike Avila, who has a low average but some power, Holaday has a high average with no power.  Considering that Holaday has a 78 wRC+ and a 77 OPS+, it's obvious which combination produces a better offensive player.  Given Holaday's .361 BABIP, it's likely that his high average has been luck driven anyway.  The eye test shows that Holaday isn't an elite defensive catcher either.


Cabrera is batting .306/.364/.534 with a 142 wRC+.  Even with his home run power down from the pace we saw the last 2 years, he's still an offensive force.  However, he's not in the "elite" class anymore with six first basemen having a better wRC+.  He does rank 3rd in fWAR, though, due to having the best defensive rating among all first basemen, a complete 180 degrees from his third basemen rating.

Ian Kinsler has the highest fWAR among all Tiger positional players at 3.5 wins.  He's hitting .303/.337/.470 and his 121 wRC+ ranks 5th among all second basemen.  The only issue with Kinsler's offensive performance is his 4.4% walk rate; only Hunter has a lower walk rate among everyday Tiger players.  Kinsler is walking almost half as much as he was from the last 2 years.  Defensively, he's been one of the best at his position.  Definitely worthy of an all-star selection.


Due to injuries (Jose Iglesias), bad trades (Alex Gonzalez) and lack of production (Romine), the Tigers were forced to call up rookie Eugenio Suarez a year sooner than they anticipated.  He has responded with a .265/.345/.429 batting line with an above average 116 wRC+.  Lately though, he's shown signs that he may not quite be ready; since June 15th, he's batting .231/.302/.282 with a 65 wRC+.  Defensively he's been great, at least going by the eye test.  

Nick Castellanos - D

Castellanos has hit for a decent .262/.307/.394 batting line with a slightly below average 91 wRC+.  What really brings his rating down is his defense.  Castellanos has been the worst defensive third basemen in baseball, and it's not even all that close.  His horrible defense has lowered his fWAR to a below replacement level -0.2 wins, which by all means warrants an F rating.  However, there have been moments where he has shined and I'm cutting him some slack for being a rookie.

Andrew Romine - F

Romine has hit for a pathetic .217/.277/.259 batting line.  Out of everyone with at least 150 plate appearances this year, only 7 players have a worse wRC+ than Romine's 49.  Many of them have either been sent back to AAA or DFA'd.  His defense would have to be great to earn a better than a failing grade, and it hasn't been going by my eye test.  


J.D. Martinez - A+ 

J.D's 182 wRC+ is higher than any other Tiger hitter this year.  Out of everyone with at least 200 plate appearances this year, J.D. has the highest batting average (.346), SLG (.654) and wRC+ (1 point above Mike Trout's).  He is one home run short of Cabrera's total despite not being called up until April 21st.  If you include the 10 home runs that he hit in AAA, J.D. has hit 23 home runs altogether this year, which is 2 more than V-Mart's total.  Even his below average defense isn't enough to lower his perfect rating.  

Rajai Davis - B

Davis has been overall solid for the Tigers this year, hitting .296/.338/.432 with a 116 wRC+.  He has provided some speed to the Tigers lineup (something in which they've lacked the last couple of years) with 24 stolen bases this year, which ranks him tied for 6th in all of baseball; only Jose Altuve has more in the American League.  His defense has been below average, but not exactly horrible.  

Austin Jackson - D

This was supposed to be Jackson's big breakout season and it has been anything but so far.  His offensive production is very similar to Castellanos' with a batting line of .256/.317/.373 with an 89 wRC+.  His defense, once elite, is now average to slightly below average, not good enough to bring up his rating.  

Torii Hunter - D-

Hunter has been an average hitter this year with a 101 wRC+ and a 100 OPS+, hitting .272/.293/.450 overall.  The one downside to his offensive production is his minuscule 2.8% walk rate.  If defense weren't a thing, Hunter would get a solid C rating.  However defense cannot be ignored and Hunter has been awful at it this year.  FanGraphs gives him a rating of -15.0 for his defensive component of WAR, which is the worst in baseball.  Not just outfielders, but everyone.  His defense is so bad, his fWAR is -0.6, even with average offensive production, which is the worst on the Tigers among positional players.  The only thing preventing him from an F rating is his veteran presence , leadership qualities and all those other intangibles.     

Don Kelly - F

Kelly is batting .258/.333/.309 with a 79 wRC+.  The only redeeming offensive quality from Kelly is that he's 2nd on the team with a 10.2% walk rate.  His power is nonexistent with a .058 ISO.  He has average to slightly below average defense.  Altogether he's worth -0.2 fWAR.  

Kelly's flexibility is not going to be able to save him when Dirks returns from the disabled list.  The only other likely candidate is Andrew Romine and the only thing saving him is that he's the only player able to backup the shortstop position.  Adding Dirks basically gives the Tigers 6 outfielders and that's one too many with Kelly being the worst of the bunch.  I don't see the Tigers being bold and DFA-ing Hunter.

Designated Hitter:

Victor Martinez - A+

V-Mart is having a career year with a batting line of .328/.391/.599 with 21 home runs.  He's only 4 home runs off his career high with a half a season left to play.  He has exceeded my expectations even when I amended my prediction about a quarter of the way through the season.  Among qualified batters he's 4th in baseball with a 165 wRC+ and 2nd only to Mike Trout in the American League.  It's a shame that he's battling injuries right now as I'd like to see him make a bid for 40 home runs this year.  

Starting Pitching:

Max Scherzer - A

The only Tiger pitcher going to the All-Star game, Scherzer has the highest fWAR among Tiger starters at 3.1 wins.  His fWAR ranks 10th in baseball and 9th in the American League.  His 2.96 FIP and 2.97 SIERA suggest that his ERA of 3.35 is higher than it should be.  He ranks 3rd in all of baseball with a 10.4 K/9.

Anibal Sanchez - A- 

Sanchez has the lowest ERA on the Tigers starting staff at 3.04.  This ranks him 26th in baseball and 11th in the American League.  His fWAR is 2.4 despite having the same FIP as Scherzer's 2.96, due to a lack of innings.  His WHIP of 1.04 is the lowest on the Tigers current roster, but his 6.7 K/9 is lower than it has been the last 2 years (10.0 last year and 7.7 in 2012). 

Rick Porcello - B

Porcello was making a good bid to get on the All-Star team up until his last 2 starts.  He was even on the final vote, but his nationally televised start last Sunday didn't do him any favors, when he gave up 7 ER in 5 2/3 IP.  His ERA is the lowest of his career at 3.39 but lower than his 3.94 FIP and 4.22 SIERA.  In fact, his FIP and SIERA are higher than they were a year ago, suggesting a bit of good fortune for Porcello.  One sign that suggested that this year would be Porcello's big breakout year was his 7.2 K/9 that he put up in 2013, but that has all disappeared to a 5.0 K/9 in 2014.  His groundball rate is currently at 48.2%.  It has never been below 50% at any other year.  This is an important stat for a sinkerball pitcher like Porcello.

Drew Smyly - C-

The league ERA is currently 3.81, Drew Smyly's ERA is at 4.00.  The league WHIP is currently at 1.29, Smyly's WHIP is 1.37.  The league average K/9 is at 7.7, Smyly's K/9 is currently at 7.2.  Factoring in park adjustments, he's right around league average with a 104 ERA+ and a 99 ERA-.  However, his FIP is at 4.46 for an FIP- of a below average 111 (minus stats on FanGraphs means over 100 is below average).  His SIERA of 4.14 is closer to his ERA, though.  Slightly below average altogether gives him a slightly below average score.    

Justin Verlander -  D

Out of 94 qualified starting pitchers, Verlander ranks 88th in both ERA (4.88) and WHIP (1.46) and is tied for 83rd in ERA+ at 85.  From May 14th to June 16th Verlander posted a 7.83 ERA, a 1.85 WHIP and a 5.61 FIP.  Not too many starters would have been able to survive that stretch.  Overall his FIP is 4.02 and SIERA is 4.39 showing that he probably hasn't been as bad as his ERA suggests.  His FIP- is 101, which is very slightly below average.  The eye-popping stat is his 6.7 K/9 when we're used to seeing it at around 9.0.  

Relief Pitching:

Joba Chamberlain - A

Joba has easily been the Tigers best reliever this year with a 2.63 ERA, a 2.47 FIP, a 2.66 SIERA and a 9.6 K/9.  However, the most important stat for a reliever just may be RE24 as it takes into account the situation (since relievers are constantly brought in and taken out in the middle of an inning).  Joba's 6.29 RE24 is the best on the Tigers staff among relievers with significant amount of innings.   His 17 shutdowns also leads Tigers relievers 

Al Alburquerque - B+ 

Alburquerque has been the 2nd best Tigers reliever with a 2.91 ERA, 3.49 FIP and a 2.64 SIERA.  His K/9 is still an impressive 10.1.  He's 2nd on the team with a 2.30 RE24 and 3rd in shutdowns with 9.  The big improvement from Alburquerque is the cut down in walks, at a rate of more than half from last year.  

Phil Coke - D

With a 4.59 ERA and a 1.50 WHIP, Coke has not been good by standard measures.  His 4.01 FIP and 3.28 SIERA suggest that he's better than his ERA indicates, though.  However, his RE24 is -1.35.  When you are contributing negative runs to the team, you are on the verge of failing.

Joe Nathan - D-

Among qualified relievers, Nathan is 149th out of  155 in ERA at 5.61.  His ERA is the highest among all relievers who are still closing.  Only 10 qualified relievers have posted a worse RE24 than Nathan's -5.93.  His FIP of 4.33 and SIERA of 3.38 suggest a bit of bad luck, which is a good sign going forward.  He's still striking out guys at a high rate of 9.4 K/9.  

Ian Krol - F

Even though Krol has a better ERA (4.44) than Coke and Nathan, there are still reasons to believe that Krol is the worst reliever in the Tigers' bullpen.  His 1.59 WHIP is worse than either Coke's or Nathan's and his FIP of 5.76 is not only the worst on the Tigers, but the worst among any reliever who has thrown at least 25 innings this year.  Krol has a -4.55 RE24; only Nathan has posted a worse number in the Tigers' bullpen.  Krol is tied with Coke by allowing 10 inherited runners to score; only 7 relievers have allowed more.  

Blaine Hardy and Chad Smith get an inc. since they haven't pitched enough for me to properly evaluate them.  

Thursday, July 3, 2014

Is Rick Porcello an All-Star?

Rick Porcello just finished back-to-back complete game shutouts, giving him career best stats in ERA (3.12), WHIP (1.13) and batting average against (.241).  The 2014 all-stars will be revealed on Sunday, so Porcello's stats are complete; he has no more starts before the rosters will be announced.  There are only so many spots available and some pitchers are having just as good of a season or better than Porcello, therefore it isn't really a slam dunk he'll make it.  Also, every team must be represented and past performance could also be a factor (Porcello has never been an all-star before).  So how good of a chance does Porcello have in making it this year?  

There are usually 7-8 starting pitchers selected for the all-star game, with 5 of them selected by the player's vote.  The other players are chosen by the manager while making sure every team is represented.  Right now I believe there are 3 locks: Masahiro Tanaka, Felix Hernandez and Mark Buehrle.  All have double digit wins, all are in the top 4 in ERA and in the case of Hernandez and Buehrle they have been all stars before.  Tanaka is in his first year in MLB but he's tied with the league lead in ERA and wins.  

This leaves 5 spots available, with Porcello certainly in the mix.  If wins were the most prominent stat in selecting the pitchers, Porcello would get voted in as he's tied for the league lead with Tanaka with 11 wins.  However, we're in the age of advanced stats and wins are becoming less and less looked at as the holy grail of pitching stats.  Even with players making the selection, they could look beyond wins.  Porcello is currently 12th in the American League in ERA, meaning he'd be on the outside looking in.  He's 6th in rWAR, but tied for 17th in fWAR.  

Now would be a good time to make sure every team is represented.  Some teams will have a starting pitcher as their best option for a roster spot and so will take up 1 less spot available for Porcello.  First there are the Rays.  Evan Longoria and Ben Zobrist aren't exactly having all-star years, but might go based on precedence.  Chris Archer just might be the most deserving on that team.  Will Michael Brantley make it with the Indians?  If not, Corey Kluber will get chosen.  There's also a similar situation with Jose Altuve and the Astros.  If for some reason he doesn't get selected, then Dallas Keuchel will go (there's also the possibility that George Springer will go despite not being with the club all year).

Out of those situations, Chris Archer has the best opportunity to take a roster spot away from a more deserving candidate, so now we are down to 4 roster spots.  Here is a list of candidates that Porcello is competing for a roster spot:

Rick Porcello
Dallas Keuchel
Corey Kluber

The Red Sox won the World Series last year, so John Farrell will select his own player Jon Lester (it's just the way it is).  I can't imagine Yu Darvish not going either.  After that, Rick Porcello might just be the next deserving candidate, although there is certainly a case to be made for any one of these pitchers.  

Another thing that needs to be considered is the rule that makes someone unavailable to pitch in the all-star game if they had pitched the Sunday before.  Those pitchers get replaced by someone else.  I don't know what everyone's pitching rotation will look like in the next week (and even then it could get changed) but Porcello is currently slated to start the Saturday before, making him eligible to pitch.  So even if he doesn't get initially selected, Porcello is in a good position to replace someone else if they can't pitch in the game (not to mention the possibility of someone getting injured).  

All things considered, I'd be shocked if Rick Porcello wasn't an all-star this year.  

Wednesday, June 11, 2014

Austin Jackson Is Not a Middle of the Order Hitter

When the Tigers signed Rajai Davis and traded for Ian Kinsler during the off-season, it was evident that Austin Jackson would get a new role in the batting order.  It seemed like a good time to test him as a middle of the order hitter.  He's just entering his prime at age 27; he's lowered his strikeout rate over the past couple of years; and he's shown some power before, hitting 16 home runs in 2012.  

The Tigers and manager Brad Ausmus also thought it was a good idea to try to make him a middle of the order run producer.  Jackson has played 50 of his 57 games batting either 5th or 6th.  The results, however, have been disappointing.  He's only batting .254 with 3 home runs and 18 RBI.  His 93 wRC+ is below league average and his ISO of .132 is lower than his previous two years.  He does lead the league in sacrifice flies, though with 7.  However he's on pace to hit less than 10 home runs with around 50 RBI.  

His struggles have been even more pronounced recently.  After having a decent April in which he hit .307/.391/.520, Jackson has hit .223/.273/.308 over his last 35 games.  

Looking deeper into the stats, his batted ball data shows that Jackson is hitting more fly balls this year, probably as a result of changing his approach in an attempt to hit more home runs.  Unfortunately, it's not working.  According to FanGraphs:


Jackson's home run to fly ball ratio hasn't been this low since it was 3.3% in his rookie year.  Jackson has always had a high BABIP, but that usually comes with a high line drive rate and a high ground ball rate.  With a high ground ball rate, Jackson can beat out infield singles, raising his BABIP.  Hitting ground balls at a rate of 33.5% has given Jackson little opportunity to get infield hits, only 2 so far this year.    

Plate disciple numbers also show a slight change, but in a positive way.  According to Pitch f/x:

Year Swing% Z-Swing% O-Swing%

Jackson's 22.3% out of zone swing percentage is the lowest of his career.  This has resulted in a career-best strikeout rate of 17.9%.  His walk rate is also up from last year at 9.8%.  

Another positive is that Jackson is hitting left-handed pitching really well this year, .320/.410/.440 in 61 PA.  Unfortunately, this also means that Jackson has struggled mightily against right-handed pitching, .232/.287/.368 in 174 PA.  This is a complete reversal of what we saw in 2013 when Jackson had a .296/.345/.439 line against right-handed pitchers and a .213/.319/.363 line against left-handed pitching.  So maybe this new approach should only be used when facing a left-handed pitcher.

Baseball is as much of a mental game as it is a physical game.  The first step has to be to take Jackson out of the 5th and 6th spot and put him in a position where he doesn't think he has to be a run producer.  Right now that should probably be 8th or 9th but as he improves, batting 2nd might be the ideal spot, right after Kinsler.  Jackson needs to go back to doing what made him successful: a line drive/ground ball hitter instead of the flyball hitter that he has turned into.  

Before this season, many fans wanted the Tigers to sign Jackson to a long-term deal while he's still young.  That would mean a similar deal to the one the Yankees gave Brett Gardner, which is 4 years and $48 million with a 5th year option of $12.5 million.  I wonder if it would be better situation for the Tigers to use that money instead for a legitimate middle of the order hitter.  

Monday, May 12, 2014

Victor Martinez' Power Surge and Regression

In his last 7 games, Victor Martinez has hit 4 home runs, bringing his total to 8 HR on the year.  V-Mart ranks tied for 14th in all of baseball and 7th in the American League in home runs.  He leads the Tigers by 3 over Miguel Cabrera.  This is all surprising because Victor Martinez isn't really a home run hitter.  The most home runs he has hit in any given year was 25 in 2007 and he's on pace to pass that mark by about 13-14.  Through his first 33 games, here is how many home runs V-Mart has hit in each year:

Year Home Runs

2008 was an injury-shortened year and he missed all of the 2012 season also due to injury.  There are a couple of 6's and 5's in there, so he has come close to this pace in the past to start the year.  It's worth noting that Martinez was still was catching often through the 2010 season, so the grind of catching could have slowed down his pace in the past.  However, even though he's mostly DHing now, he is much older, so it's still unlikely that he'll maintain his current pace.  However, it's still fun to look at the numbers.

Year HR% HR/FB

The HR/FB ratios are taken from FanGraphs.  

Martinez has hit 0.242 home runs/game, on pace for 39 home runs given 162 games.

Martinez has a 5.8% HR rate, on pace for 38 home runs given 650 plate appearances.

Martinez has a 17.0% HR/FB ratio, on pace for 38 home runs given 221 fly balls*.  

*V-Mart is on pace for about 221 fly balls in 2014.  He has a 39.2% fly ball ratio, an 8.7% walk rate and only a 4.3% strikeout rate and 0 hit by pitches.  

Batted Balls = plate appearances - walks - strikeouts - hit by pitches.  

Given 650 plate appearances, that's 57 walks and 28 strikeouts.  That's 650-57-28  = 565 batted balls.  565 * 39.2% = 221 fly balls (rounded).  

We can start here with the regression.  V-Mart's strikeout rate is the lowest of his career.  Over his prior 3 years (2010-2013), his strikeout rate was at 9.2% and career-wise it's at 10.7%.  This year, it's less than half of that.  His strikeouts have been trending downward, but it's unlikely it'll remain at his current low pace.  Let's say he finishes the rest of the year at 8.5%.  Given 650 plate appearances, that's (650-138 = 512 * 8.5% = 44 more strikeouts for a grand total of 50.  

Martinez' walk rate over his prior 3 years is at 7.8%.  His career mark is at 9.3%.  His current 8.7% rate is right in the middle.  It's reasonable that he can keep this pace for the rest of the year, so I'm leaving this one alone.  

Changing his strikeouts to 50 and keeping everything else equal, that's 543 batted balls  (650 PA - 57 walks - 50 strikeouts).  At his current pace of 39.2% fly ball ratio, that's 213 fly balls.   At 17.0% HR/FB ratio, that drops down to 36 home runs.  

What about his 39.2% fly ball ratio?  Over his prior 3 years it is at 36.6% and his career mark is at 36.2%.  While it's not glaringly higher, let's regress it to 36% anyway.  543 * 36% FB%= 195 fly balls * 17.0% HR/FB = 33 home runs.  

Now the big regression of his HR/FB rate.  Over his prior 3 years, it's at 8.4% and his career is at 10.2%.  He spent his 2010 season with the Red Sox and while playing half his games in Fenway, it was at 10.7%.  Over his last 2 years with the Tigers it was at 7.3% and 7.2%.  Let's say he only accomplishes 7.5% HR/FB the rest of the season.  He's currently at 47 fly balls, so 195-47 = 148 * 7.5% HR/FB = 11 more home runs this year, or 19 total.  

Victor Martinez has had a 2.6% home run rate over his prior 3 years, close to his 2.7% career mark.  Over his last 2 years with the Tigers it's at 2.0% and 2.1%.  Given 650 PA on the year or 512 more for this year: at 2.6% HR%, that's 13 more (21 total) and at 2.1% HR%, that's 11 more (19 total).  

In my 2014 preseason prediction for Victor Martinez, I gave him 13 home runs.  If I were redoing them, I would up it to an optimistic 20.  V-Mart is enjoying a bit of a power surge right now, but it's very likely unsustainable.

Friday, May 9, 2014

What Happens When Rick Porcello Is Not Getting Ground Balls

When Rick Porcello gets ground balls, he prevents runs.  Just look at this table, sorted by highest ground ball rate (using FanGraph's numbers):

Year GB% ERA

It's almost a perfect correlation that the higher Porcello's ground ball rate, the lower his ERA.  In fact, take out his rookie season and his current season and it is a perfect correlation.  The chart below shows Porcello's first 5 seasons in MLB and the trend line:

So when Porcello is showing his lowest ERA along with his lowest ground ball rate in 2014, it raises a red flag, even if it is only in 6 starts.  Using the formula of y = -0.0451x + 0.7321, with a GB% of 43.9%, we would expect an ERA of 6.50.  With an ERA of 3.49, we would expect a GB% of 57.5%.  Did he change his approach?  Is he just getting lucky?  Is it just a 6 game anomaly?

Rick Porcello has an 18.2% strikeout rate, a 4.1% walk rate and a 2.0% home run rate which results in a 3.16 FIP, the lowest mark in his career.  FIP uses strikeouts, walks and home runs and shows what a pitcher's ERA should look like.  

However, he has a 29.8% line drive rate and a 26.3% fly ball rate to go along with his 43.9% ground ball rate, which results in a 4.83 tERA.  tERA is another ERA predictor, but uses batted ball information.  SIERA kinda uses a combination of both FIP and tERA and says Porcello's ERA should be 3.50 (which is the closest to his actual 3.49 ERA).  His ERA estimators are giving off mixed signals.   

The 29.8% line drive rate is the highest of his career:

Year LD% GB% FB%

Conveniently, Baseball Reference gives the exact same batted ball figures (FanGraphs and Baseball Reference use different sources for their batted ball data and usually they disagree on few batted ball types).  I have to switch to Baseball Reference here since FanGraphs doesn't go as deep into batted ball data for pitchers as they do for hitters.  According to B-Ref, Porcello has a .559 BAA on line drives in 2014.  For his career, his BAA on line dives is at .696 and typically it's around .700.  Simply put, Porcello is very fortunate that more of his line drives haven't fallen in for base hits and it's keeping his ERA low.    

Going to Brooks Baseball, we can see exactly what pitch is causing Porcello's lack of ground balls:

Porcello's ground balls on 4-seam fastballs are usually in the mid-40% range, but it has dipped all the way down to only 5.9% so far in 2014.  Conversely, his fly ball rate on 4-seam fastballs has gone up:

Porcello's lack of ground balls, high line drive rate and crazy 4-seam fastball trend hasn't hurt him yet, but it's something to keep an eye on in his next start and going forward.  I don't believe Porcello can continue to have success with this combination.  

Monday, April 28, 2014

Alex Avila Was Clutch in 2013

What does one do when there's two days of no baseball (thanks a lot, rain)?  Look through FanGraphs' list of stats of course!  I was in the midst of comparing Alex Avila to the other catchers in the league (and he was right in the middle of the pack, where you'd expect a 92 wRC+ hitter to be).  When I got to the "Win Probability" tab, I noticed 2 things.  One, hey, there's a clutch stat!  And two, Alex Avila is sitting right on top at 2.09, making him the most clutch catcher in 2013.  Pretty neat, huh?

Looking deeper into FanGraphs' glossary, I got the formula to how they calculate this stat:

Clutch = (WPA / pLI) – WPA/LI

Avila had a WPA of 1.02, a pLI of 0.89 (1.02/0.89 = 1.15) and a WPA/LI of -0.95 (1.15 - -0.95 = 2.10).  There's probably a rounding issue here.

So what do these stats mean?  WPA is Win Probability Add.  It's a measure of the change in win expectancy from the time a batter enters that batter's box until the end of play.  Without getting too technical, there's a win expectancy chart that shows the percentage of how likely a team is going to win the game at any particular moment in the game.  For example, say a team has a 45% chance of winning a game.  Then a batter hits a HR.  Now the team has a 75% chance of winning.  The difference (0.75 - 0.45 = +0.30) gets credited to the player.  You may have already seen this in chart form:

Source: FanGraphs

pLI is the player's Leverage Index in all situations.  It attempts to quantify the "pressure" aspect of the game by factoring in the inning, the score, the number of outs and the number of runners on base.  Think of bases loaded in the 9th inning of a tie game as a really high leverage situation and a 13-0 blowout in the 5th inning a really low leverage situation.  Neutral is given a 1, "high leverage" is considered to be 1.5 and above and "low leverage" is below 1.  Avila's 0.89 is right around 1, which is to be expected.

WPA/LI is context neutral wins and is calculated on an individual play basis and then added up during the season.  During the game, some players will see more at bats in higher leverage situations than others, so this stat puts everything on a level playing field.  Sometimes a walk is just as valuable as a HR, so this stat will show that.

The subtraction of these two will result in showing only high leverage situations.  So what we are seeing is how much better a player performed in high leverage situations compared to how he performed in low and medium leverage situations.  FanGraphs also gives splits on these situations, so we can see them in more traditional stats:

Low Leverage
Medium Leverage
High Leverage

And it's clearly noticable that Avila performed much better in high leverage situations than in low and medium leverage situations.  The difference between them was better than the difference of any other catcher last year.  And better than any other Tiger batter last year.  In fact, Avila was the most clutch player of anyone with at least 300 plate appearances last year.    

One last thing to keep in mind - there is no predictability value here.  Just because a batter preformed well in high leverage situations one year, doesn't mean he'll continue to perform that way every year.  This is why several people claim there is no such thing as a clutch hitter.  To prove this, look at how Avila has performed in high leverage situations in the past:

High Leverage AVG OBP SLG wRC+

While Avila performed pretty well in High Leverage situations in 2012, in 2011 he was pretty poor.  If you remember, 2011 was Avila's big breakout year (.295/.389/.506, 140 wRC+ overall).  

FanGraphs says that this is a good storytelling stat.  And that's all this is, a good story.