Using WPA to grade bullpen management, part twoby Dan Lependorf
November 23, 2012
In my last article, I outlined a method of analyzing bullpens by making a small tweak to the inside of the WPA Clutch metric. To quickly recap, Clutch gives the difference between how a player performed and how that player would have performed in a luck-neutral context-independent environment. Clutch was designed for batters who cannot choose when and where to bat, so the first term has a pLI denominator that puts every batter on an equal footing regarding the number of high leverage plate appearances they participated in.
But since we're measuring relievers, who don't get equal amounts of leverage by design, the pLI denominator excises some pretty useful information. By stripping away the pLI denominator from the first term, the Clutch metric changes what the stat is measuring. By taking it out, we arrive at a number that is a sum of how a player performed in the clutch added to how efficiently a manager deployed his relievers. To put it in mathematical terms:
If we want to remove player effects and isolate the manager’s contribution, all it takes is some simple algebra.
Which finally leaves us with this.
It's really quite simple. WPA gives a total picture of a player's contributions to a team's win. Subtracting context-independent WPA/LI leaves behind only the effects from the timing of game events. Subtracting away Clutch from that total pares WPA down even further, so all that remains is how a manager helped or hurt his team with his bullpen management decisions.
And now, of course, the fun part. Here's 2012's leaderboard.
I find this absolutely fascinating. Two teams that surprised everyone by making the playoffs are ranked one and two, with bullpen management responsible for five wins over the course of the season. Keep in mind that this doesn't mean that Buck Showalter and Bob Melvin were five wins better than the average manager. Zero wins would mean that a manager's bullpen management was no better than drawing names out of a hat, and as you might imagine, most managers are better than that. The average, as counted from the beginning of WPA data on Fangraphs, is a hair shy of two wins.
So what does it all mean? Managers who use their bullpens efficiently generally add somewhere around two or three wins to a team's season total, as compared to an average two-win manager. By the same coin, managers with inefficient bullpen management can cost their teams a win or two by using the wrong pitchers in critical situations.
References and Resources
All data from Fangraphs (1974-2012).
My full data set is here. It contains WPA, Clutch and Manager figures for every team from 1974 to the present.
Dan can be contacted here (email) or here (twitter). He welcomes all comments, even offers for cheap male enhancement pills and winnings from lotteries he didn't realize he had entered. (He really wishes you wouldn't, though.)