Arbitrary Endpoint Leaderboards: May Hitters

A couple of weeks ago, I waxed idly on the degree to which April numbers — and the narratives they create — seem capable of occupying an inordinately large space in the baseball fan’s mind, even as the season progresses. Reader Mike noted in the comment thread of that post — nor do I have any interest in contradicting him — that this is due to what is called the Primacy Effect. The Primacy Effect is, according to Wikipedia, “a cognitive bias that results in a subject recalling primary information presented better than information presented later on.”

While the author has no intention of speaking for the reader, I don’t think I’m being particularly controversial by suggesting that the Primacy Effect does seem to play a part in the way we remember and reflect on a season, whether in progress or after the fact.

As a means to pushing back against this bias, I’ve presented below two leaderboards for May hitters — one a simple WAR leaderboard, the other an Expected wRC+ leaderboard — with notes on same. Insofar as basically all endpoints are arbitrary — a point noted by my colleague Eno Sarris last August — these May numbers aren’t necessarily more “important” than either their April or full-season counterparts. Still, they do reveal what has happened over the most recent stretch of meaningful baseball games, which has some value in itself.

Offensive WAR Leaders
Here are the leaders, among field players, in WAR for May:

Notes
• I still believe — despite managing editor Dave Cameron’s comments to the contrary on yesterday’s edition of FanGraphs Audio — I still believe that Mike Trout is in the conversation with Bryce Harper as the Hope for Our Future. With Bobby Abreu having been released and Vernon Wells on the DL and Torii Hunter away from the team for personal reasons, Trout was able to secure regular playing time in May. As the above indicates, he took advantage of that opportunity. Of note: ZiPS — which, like other projection systems, is generally rather conservative — projects the 20-year-old Trout to end the season with a 4.8 WAR.
• Everything about Giancarlo Stanton’s game has been better in May than in April — not only his raw home-run totals (11 vs. 1) and home-run per fly-ball rate (29.7% vs. 6.3%), but also his plate-discipline numbers. Here’s April, for example: 5.2% BB, 26.0% K. And here’s May: 13.2% BB, 19.8% K. It’s possible that return of Stanton’s power has been the cause of his increased plate discipline: while his O-Swing rate was actually slightly higher in May (30.3%) than April (29.6%), according to PITCHf/x, Stanton was starting to see fewer pitches in the zone (45.7% in May vs. 50.0% in April). Stanton is projected to post a 3.9 WAR over the rest of the season, per ZiPS, the fifth-best mark by that measure.
• Click here to see all of May’s WAR leaders.

Expected wRC+ (xRC+) Leaders
This is essentially a version of Bradley Woodrum’s Should Hit formula (itself more or less a FIP for hitters, but with BABIP included) but using regressed (as opposed to raw) home-run, walk, and strikeout rates as the inputs. Also, BABIP is replaced by expected BABIP (xBABIP), per the formula (adjusted for 2012 league averages) proposed by user slash12 at Beyond the Boxscore in 2009.

The idea here is to estimate something like a player’s true talent over the course (in this case) of the last month.

Notes
• Even witout a regressed line, Detroit shortstop Jhonny Peralta has played quite well in May. To wit: .263/.385/.425, 130 wRC+, 0.7 WAR. That, however, is with only a .274 BABIP, while Peralta’s career mark is actually .313. Peralta’s excellent May has likely been obscured by the fact that his April, during which he posted a 61 wRC+ and -0.1 WAR in 78 plate appearances, was so poor.
• San Francisco outfielder Gregor Blanco was a freely available talent heading into the season. Now, he’s posted a 1.5 WAR over his first two months as a Giant, where he’s settled into the starting right-field role. The regressed numbers suggest that Blanco’s May has been more impressive than even Melky Cabrera’s, the latter of whom has done this over the last month: 123 PA, .435/.463/.661 (.480 BABIP), 211 wRC+, 1.9 WAR.
• Click here for a complete list of May’s xRC+ leaders.