June 2, 2008

WPA Through May

Win Probability Added (WPA) measures how much impact specific plays had on the outcome of each game and assigns that value to the individual players responsible. For example, when evaluated by WPA within the context of each game hitting a grand slam in the fifth inning when the score is 10-2 has less value than drawing a walk in the eighth inning when the score is 5-5. Similarly, striking out to lead off a game is seen as less damaging than striking out down a run in the bottom of the ninth inning.

There are much better and longer explanations of WPA than that one, of course. If you're interested in learning more, Dave Studeman's WPA primer at The Hardball Times is a good place to start, and both Fan Graphs and Baseball-Reference.com offer tons of information on the subject. It's far from a perfect stat and isn't meant to predict how valuable a player will be or even definitely prove how valuable each player has been, but WPA is an interesting tool to use in looking back at what has already taken place.

It's important to note than WPA doesn't measure any defensive contributions, which means that strong defenders don't receive full credit for their value. Beyond that, WPA doesn't place offensive contributions in the context of position, so an .850 OPS from a catcher or shortstop is treated the same as an .850 OPS from a designated hitter or left fielder. There's nothing that can be done about measuring defense via WPA, but it's relatively easy to put the numbers in better context by using positional adjustments.

With the help of Fan Graphs creator David Appelman, I've taken the Twins' raw WPA totals through May and adjusted them based on the MLB average at each position. Most adjustments are minimal, but starters are given a boost relative to relievers and hitters who play up-the-middle positions are given a boost relative to hitters who man corner spots. The end result is a sort of adjusted WPA (adjWPA), but before getting to that let's first take a look at the raw season totals through May 31:

HITTERS                PA      AVG      OBP      SLG      WPA
Joe Mauer 212 .317 .405 .389 1.45
Justin Morneau 236 .305 .377 .495 1.25
Alexi Casilla 61 .340 .417 .520 0.52
Craig Monroe 106 .235 .292 .459 0.36
Howie Clark 8 .250 .250 .500 0.27
Matt Macri 4 .667 .750 .667 0.11
Brian Buscher 9 .250 .333 .375 -0.01
Pitchers 9 .375 .375 .375 -0.02
Denard Span 34 .258 .324 .258 -0.11
Mike Lamb 179 .255 .285 .345 -0.18
Jason Kubel 182 .241 .280 .388 -0.26
Nick Punto 59 .264 .322 .340 -0.29
Matt Tolbert 90 .265 .307 .337 -0.34
Carlos Gomez 219 .282 .315 .411 -0.37
Brendan Harris 198 .253 .328 .335 -0.60
Adam Everett 83 .189 .235 .324 -0.68
Mike Redmond 34 .226 .265 .290 -0.78
Michael Cuddyer 168 .232 .292 .323 -0.83
Delmon Young 226 .264 .323 .337 -1.11

TEAM TOTAL 2117 .267 .324 .381 -1.67

Joe Mauer's team-leading 1.45 WPA comes primarily from a huge May, as he hit .333/.442/.387 in 113 plate appearances to produce 1.33 WPA for the month. To put that in some context, consider that only four other AL hitters (Manny Ramirez, Josh Hamilton, Carlos Quentin, Hideki Matsui) have produced more than 1.33 WPA for the entire season. Justin Morneau's second-ranked 1.25 WPA is more evenly split, with 0.63 WPA in April and 0.62 WPA in May.

Mauer and Morneau have carried the offense to an extreme degree, producing 2.70 WPA through two months while the other hitters combined for -4.37 WPA. Along with Mauer and Morneau, Alexi Casilla and Craig Monroe are the only hitters on the team with double-digit plate appearances and positive WPA. Casilla hit .340/.417/.520 in May after spending all of April at Triple-A, while Monroe fares well in WPA despite a mediocre .235/.292/.459 overall line thanks to several key hits in both months.

Michael Cuddyer hit relatively well in April, but posted a team-worst -0.47 WPA by coming up empty in several crucial spots. Cuddyer had a similarly poor -0.36 WPA in May, but this time it simply came from hitting .212/.273/.297. Cuddyer's -0.83 WPA through two months ranked second-worst on the team, with Delmon Young bringing up the rear at -1.11 WPA. That total ranked eighth-worst among AL hitters and Young was at "only" -0.10 WPA through April, so he produced a ghastly -1.01 WPA in May alone.

Carlos Gomez's -0.34 WPA in April made sense given his .265/.279/.373 line, but his -0.03 WPA in May looks off after he hit .299/.348/.449. WPA is about how you perform, but also how you perform within the context of each game and how that impacts your team's chance of winning. Gomez was much better than an average hitter in May, but WPA shows that his hitting had an average impact on the Twins' wins and losses. There's no shame in that, because "average" in WPA is the equivalent to a .500 team.

PITCHERS               PA      AVG      OBP      SLG      WPA
Joe Nathan 89 .238 .281 .333 2.01
Nick Blackburn 302 .305 .341 .415 1.25
Matt Guerrier 137 .256 .338 .364 0.81
Dennys Reyes 71 .281 .343 .359 0.71
Bobby Korecky 40 .222 .300 .389 0.60
Scott Baker 132 .244 .273 .409 0.57
Craig Breslow 5 .000 .000 .000 0.15
Glen Perkins 131 .303 .341 .467 0.13
Kevin Slowey 136 .233 .272 .457 0.09
Pat Neshek 56 .240 .291 .460 0.03
Brian Bass 160 .308 .375 .545 -0.15
Juan Rincon 113 .245 .360 .340 -0.57
Livan Hernandez 335 .330 .353 .494 -0.65
Jesse Crain 91 .313 .385 .500 -0.67
Francisco Liriano 56 .366 .509 .415 -0.67
Boof Bonser 296 .267 .316 .418 -1.47

TEAM TOTAL 2150 .283 .335 .434 2.16

Similar to Mauer and Morneau offensively, Joe Nathan and Nick Blackburn have carried the pitching, producing 3.26 WPA together while the rest of the staff combined for -1.10 WPA. Nathan's team-leading 2.01 WPA actually understates how good he's been, because he gets tagged with the negative credit for the fly ball that Young played into a game-tying "inside-the-park homer" last week. Even with that, Nathan ranked third among AL relievers in WPA, behind only Mariano Rivera and B.J. Ryan.

Blackburn's 1.25 WPA ranked 11th among AL starters and he produced a negative WPA in just three of his 11 starts through two months. By comparison, Livan Hernandez's -0.65 WPA ranks fourth-worst among full-time AL starters and he had a negative WPA in six of his dozen starts. Unfortunately for the Twins, Boof Bonser was one of the three AL starters to qualify for the ERA title while posting a worse WPA than Hernandez through May, ranking dead last in the league at -1.47.

What's amazing about Bonser's league-worst WPA is that he actually contributed positively with 0.29 WPA in April. Bonser made six starts in May, posting an 8.60 ERA while accumulating a staggeringly awful -1.76 WPA. While Bonser and Hernandez were dragging the rotation down in May, Kevin Slowey and Glen Perkins combined for 0.38 WPA. With Pat Neshek out Matt Guerrier stepped up with 0.88 WPA out of the bullpen in May and Bobby Korecky had 0.60 WPA before a demotion back to Triple-A.

After looking at the Twins' raw WPA totals through the first two months of the season, let's switch to the adjusted numbers once each player is compared to the MLB average at their respective position. In other words, Morneau is compared to other first basemen, Gomez is compared to other center fielders, Mauer is compared to other catchers, Blackburn and Hernandez are compared to other starters, and Nathan and Guerrier are compared to other relievers:

                      adjWPA                              adjWPA
Joe Mauer + 1.92 Denard Span - 0.16
Joe Nathan + 1.90 Nick Punto - 0.26
Nick Blackburn + 1.35 Carlos Gomez - 0.30
Justin Morneau + 0.86 Brian Bass - 0.31
Matt Guerrier + 0.68 Matt Tolbert - 0.33
Dennys Reyes + 0.64 Mike Lamb - 0.34
Bobby Korecky + 0.64 Jason Kubel - 0.49
Scott Baker + 0.61 Livan Hernandez - 0.52
Alexi Casilla + 0.53 Brendan Harris - 0.56
Howie Clark + 0.27 Adam Everett - 0.64
Craig Monroe + 0.23 Francisco Liriano - 0.65
Glen Perkins + 0.17 Juan Rincon - 0.68
Kevin Slowey + 0.15 Mike Redmond - 0.71
Craig Breslow + 0.15 Jesse Crain - 0.76
Matt Macri + 0.11 Michael Cuddyer - 1.10
Pat Neshek 0.00 Delmon Young - 1.35
Brian Buscher 0.00 Boof Bonser - 1.37

Making sense of the above numbers is actually fairly simple. For instance, Mauer having +1.92 adjWPA means that he added 1.92 wins compared to the average catcher offensively, while Young being at -1.35 adjWPA means that he was 1.35 wins worse than the average left fielder. Similarly, compared to the average starting pitcher Blackburn added 1.35 wins while Bonser subtracted 1.37 wins. At first glance Gomez's -0.30 adjWPA looks bad, but that's actually far from the case.

He's one-third of a win from being an average center fielder offensively, which is good for a 22-year-old. Interestingly, in Gomez's case at least WPA agrees with "normal" stats. His .282/.315/.411 line through May 31 is slightly below the MLB average of .264/.333/.409 for center fielders. Gomez is hurt by WPA failing to account for defensive contributions, because that's where much of his value comes from. Toss in his glove and there's little doubt that he's been at worst an average all-around center fielder.

Not including defense also undervalues Mauer, whose already impressive adjWPA would be even better with his work behind the plate factored in. For guys like Cuddyer and Young the opposite is true. According to WPA, even without defense in the mix Mauer was the Twins' most valuable player through May 31, followed by Nathan, Blackburn, and Morneau. At the other end of the spectrum, Bonser, Young, and Cuddyer stand out as the team's least valuable players through May 31 according to WPA.

Once you're done here, check out my latest "Daily Dose" column over at Rotoworld.

No Comments

No comments yet.

Sorry, the comment form is closed at this time.