Cubs by the Numbers: WPA (Win Probability Added)
WPA (Win Probability Added) is a stat that is more reflective than predictive, but on its basic level gives you an understanding of what a player added to the team’s chances of winning in a season. If a player hits a walk-off HR to win a tie game he impacted his team’s win expectancy from around 50% to 100%. Essentially, he increased the chances of winning 50% or .5 as a decimal. Those events add up throughout the year to give a total WPA.
As I just explained, WPA takes all the things a player does to help a team win and adds those up. Likewise, it also takes into account those things that hurt a team’s chances of winning, subtracting from the total. When a season is done you get a number that indicates how many wins a player added.
Fangraphs breaks down the stat like this for regulars:
Obviously the everyday player is going to be able to impact the outcomes of games more frequently and the platoon player not as much. The league leader in this statistic for 2014 was Mike Trout with 6.88 WPA….ok, no surprise there, but let’s see how the Cubs fared.
Anthony Rizzo led the team with 4.22 WPA, which was actually good enough to be tied for 10th place with Victor Martinez. What makes it even more impressive than simply being in the same sentence as V-Mart (who had an awesome offensive year) is the fact that Rizzo missed over 3 weeks with a back injury.
Luis Valbuena was next with 3.02 WPA, a solid total. Other interesting names of note are Chris Coghlan (1.71), Starlin Castro (0.39) and Jorge Soler, who, in his limited time of 24 games, came in 5th on the team with 0.41 WPA. I was really surprised with how low Castro’s WPA was in 2014, but in comparison to his past seasons this year was his best yet.
So how’d the kids do? As we can see, Soler did very well in his short time with the big league team, but the same cannot be said for Javier Baez or Arismendy Alcantara. Both were right around -1 WPA (Baez: -0.99, Alcantara: -1.08) for the 2014 season.
Basically, those players were bad enough that they subtracted wins from the big league team. Add in Welington Castillo’s -1.07 and the young core didn’t do much to help in 2014.
That is okay though because, as I said at the beginning, WPA is not a predictive stat but rather it’s something we can use to look back at to see how a player impacted the team overall. This stat tells us a little bit of what we already knew: Rizzo was the unquestioned MVP of the year, Valbuena and Coghlan were very good for stretches, and the kids struggled.
I have no doubt that after adjustments by Baez and Alcantara they will be able to post an average or even above-average WPA total. I’m not sold on Castillo at the moment, but there is still time. The fun thing to see next year will be what Soler can do over a full season and what damage Kris Bryant can do when the Cubs decide to let him come up and play with the big boys.