FanGraphs contains multitudes. Multiple flavors of Wins Above Replacement — one in which the pitching component is driven by FIP, the other by actual runs allowed (RA9-WAR) — for one thing. Multiple projection systems (Steamer and ZiPS) and ERA estimators (FIP, xFIP, SIERA). Multiple measures for defense, pitch selection, and plate discipline, borne of different data feeds. Multiple ways of measuring playoff odds and projected won-loss records. Multiple depth charts, now that we’ve brought Roster Resource on board. There’s a lot of cool stuff… if you know where to look.
One of the cool but relatively new and lesser-known features is our Season Stat Grid, introduced just over a year ago, and in the planning stages for longer (I know that I’m one of the people who lobbied for the tool). The grid allows the user to view 11 year worth of data in a single category, and to track and rank year-to-year totals and changes based on thresholds of plate appearances and innings. It’s hours of fun, and occasionally fuel for an article. So after highlighting the exceptional, breakout season of Rafael Devers and noting that — at the time it was written, at least — he had the majors’ largest year-over-year improvements in batting average, on-base percentage, and WAR, while ranking second in his gains in wRC+ and fourth in slugging percentage, I figured the topic was worth a league-wide look.
Towards that end, I chose 10 statistical categories where we might look for significant changes, namely the aforementioned five plus walk and strikeout rates, out-of-zone swing rate, fielding (UZR plus positional adjustment, if any) and, for a nod towards win expectancy, Clutch. To qualify, players had to reach 400 plate appearances last year and 300 thus far this year. I then took the top 30 players whose changes went in the right direction (higher in all cases except for strikeout and chase rates), awarding 30 points for first place, 29 for second, and so on. When two or more players were tied — even if it was just a virtual tie, where we can’t see what’s to the right of the displayed decimals — I split the points evenly among the tied; for example, James McCann and Yoán Moncada, who have increased their batting average by 66 points apiece, occupy the third and fourth spots and thus each get 27.5 points. I doubled the impact of WAR and wRC+ (60 points maximum), even though components of those are included elsewhere within the survey, on the belief that those two stats drive the lion’s share of our understanding as to who has improved.
I’ll make no claim that this is science, and one can certainly quibble with my choices of stats and methodology until the cows round third base and head home. For one thing, this method steamrolls any sense of scale; Tim Anderson’s 93-point improvement in batting average is worth just 2.5 points more than the gains of McCann and Moncada, with Devers’ 86-point improvement worth just one point more than the pair. Nonetheless, here’s the top 20 that my methodology yielded, with the points they received in each category:
That feels like a pretty good list, with some obvious breakouts and rebounds that have drawn varying degrees of attention. Category-wise, only a small handful of the players who improved the most in some areas — clutch, fielding, and strikeout rate, in particular — have made improvements on a similar scale in other areas, but those who scored highest via this junk-drawer methodology were the ones who tapped into those areas.
Let’s go through the top 10, lightning-round style. All stats are through Wednesday.
1. Cody Bellinger, Dodgers
After a flawed but nonetheless quite solid sophomore season (120 wRC+, 3.6 WAR), the 24-year-old Bellinger has been unreal this year after restoring his mechanics over the winter. He’s posted significant improvement in all three slash stats, cut his strikeout rate from 23.9% to 16.2% while improving his walk rate from 10.9% to 14.1%, and given the Dodgers elite defense in right field (9.0 UZR, 19 DRS) instead of playing regularly (and well) at first base. He’s one of only two players in this exercise who scored in eight out of 10 categories (the 11th-ranked Semien was the other). He entered Thursday leading the NL in homers (42) and WAR (6.9), with slight edges over reigning MVP Christian Yelich. He may well win some hardware of his own thanks to his across-the-board improvements.
2. Rafael Devers, Red Sox
As I noted on Tuesday, Devers turned in something of a dud last year (90 wRC+, 1.0 WAR), his age-21 season, but has significantly improved his two-strike approach while cutting his strikeout rate from 24.0% to 16.7%. He’s now among the top three in improving each slash stat and wRC+ (145), and his jump to 5.4 WAR is the widest in baseball. If it weren’t for some guy named Mike Trout, he’d be a true MVP candidate.
3. Carlos Santana, Indians
Santana’s one-year foray to Philly wasn’t as bad as his .229 batting average would lead you to believe (109 wRC+, 1.9 WAR), but he’s enjoyed a strong bounce back since returning to Cleveland. Thanks to a more disciplined approach, the 33-year-old first baseman’s .413 on-base percentage is second in the league, and his .552 slugging percentage is sixth. He’s been on fire lately, with six homers in a 10-game span, and leads the resurgent Indians both in homers (30) and WAR (4.4).
4. Scott Kingery, Phillies
A well-regarded prospect, Kingery flopped as a rookie (62 wRC+, -0.1 WAR), that while generally playing shortstop, a position where he had almost no previous experience as a professional. With César Hernández still a fixture at second base, the 25-year-old Kingery has bounced around the diamond again, spending most of his time in center field — where Odúbel Herrera‘s domestic violence suspension and Andrew McCutchen’s injury have thinned the ranks — and third base, where Maikel Franco has again disappointed. He’s cooled off considerably since the start of the season, but his 108 wRC+ and 2.0 WAR have put his career back on track.
5. James McCann, White Sox
McCann spent the past four years as the light-hitting regular catcher for the Tigers, meandering around replacement level, but after being nontendered following a dreadful season (58 wRC+, -0.5 WAR), the 29-year-old backstop has played his way into his first All-Star appearance. His boost from last year has been driven by top-five improvements in his slash stats, as he’s gone from hitting .220/.267/.314 to .286/.339/.470, accompanying a 98-point jump in BABIP (from .282 to .380) with a doubling of his home run rate (from once every 57 PA to once every 27 PA).
6. Yoán Moncada, White Sox
The player who topped our 2017 prospect list at age 22 didn’t embarrass himself in his first two seasons in the majors, but he’s taken some major steps forward this year. A more aggressive approach — his O-Swing% has jumped from 23.3 % to 33.2%, and his overall swing rate from 41.1% to 48.1% — has nonetheless resulted in a significant drop in strikeout rate (33.4% to 27.6%) accompanied by across-the-board improvements in slash stats; his .301/.358/.535 line, with a 134 wRC+ and 4.0 WAR, heralds his arrival as a star.
7. Ketel Marte, Diamondbacks
At bat, on the bases, and in the field, Marte has improved every major area of his game. While taking up center field (where he’s been outstanding to the tune of 7.6 UZR), he’s gone from a modest 104 wRC+ (.260/.332/.437) to a sizzling 141 (.319/.381/.574), while nearly doubling his home run output (from 14 to 27). His 5.7 WAR is topped only by Yelich, Bellinger, and Trout. Welcome to flavor country.
8. DJ LeMahieu, Yankees
In a season where every intended Yankees regular except Gleyber Torres has hit the injured list, the versatile LeMahieu has emerged as the team’s unsung hero. While splitting his time between second base (56 starts), third base (34 starts), and first base (21 starts), he’s shown that his unimpressive Coors Field stats and splits weren’t his true measure. With substantial improvements in all three slash stats (from .276/.321/.428 to .334/.381/.534) despite coming down from altitude, he’s gained 53 points of wRC+ (from 86 to 139), and with his .334 average, he’s neck-and-neck with Michael Brantley for the AL lead, giving him a shot at becoming the first player to win a bating title in both the AL and NL. What’s more, he’s hit .410/.450/.600 in 121 PA with runners in scoring position.
9. Tim Anderson, White Sox
Despite missing a month due to a right ankle sprain, and walking nearly half as often (2.6%) as last year’s meager 5.0% rate, the 26-year-old Anderson has significantly cut his strikeout rate and enjoyed a 102-point spike in BABIP (from .289 to .391), raising his batting average an major league-high 92 points (from .240 to .332) and carrying the rest of his slash stats with it. He’s already set a career high with 2.6 WAR; on a prorated basis, he’s been about twice as valuable as last season (2.0 WAR in 153 games).
10. Trey Mancini, Orioles
Though he hit 24 homers in each of the past two seasons, Mancini had enough holes in his game that he slipped below replacement level last year (-0.2 WAR, with a 93 wRC+). Driven by a nine-point drop in groundball rate (from 54.6% to 45.8%) and much-improved strikeout and walk rates, the 27-year-old Mancini has become one of the few bearable Orioles to watch. His 125 wRC+ leads the team, while his 2.1 WAR is second.
There’s more to be said about all of these players and the ones below them in the rankings, but I’ll cap it here. One surprising facet of these rankings is that it yields a complete lineup, with McCann catching, Santana at first base, LeMahieu (or Marte) at second, Anderson at shortstop, Devers at third, Mancini in left field, Kingery (or Marte) in center, and Bellinger in right, with Moncada and Marte (or his aforementioned alternatives) left over. In all, I think it’s a defensible, well-rounded list of players who have improved, and if I’m not tarred and feathered for this admittedly junk-drawer methodology, will return at some point with a similar one for starting pitchers.
Brooklyn-based Jay Jaffe is a senior writer for FanGraphs, the author of The Cooperstown Casebook (Thomas Dunne Books, 2017) and the creator of the JAWS (Jaffe WAR Score) metric for Hall of Fame analysis. He founded the Futility Infielder website (2001), was a columnist for Baseball Prospectus (2005-2012) and a contributing writer for Sports Illustrated (2012-2018). He has been a recurring guest on MLB Network and a member of the BBWAA since 2011. Follow him on Twitter @jay_jaffe.