Clayton Kershaw’s Season, Historically

Clayton Kershaw is having a fantastic season, and you didn’t need me and my numbers to tell you that. He’s going to win the Cy Young award, potentially unanimously. He has a real shot at the MVP award, perhaps only derailed by the electorate’s weird bias against pitchers.

Yet, there is something that I am seeing frequently that is bugging me enough to write about. Take this piece from the Wall Street Journal earlier this week, for example. The headline says “Clayton Kershaw is having the best season of any pitcher since 1995.” Their “fancy stats” include ERA and FIP. They are correct in pointing out that Kershaw currently has the best (raw) ERA since Greg Maddux in 1995. They’re also correct in noting that his FIP being lower makes his season more impressive, since he’s not BABIP or LOB% fluking (or otherwise) his way to his elite run prevention.

However, there is a very significant and fundamental flaw with their methodology. Clayton Kershaw is currently pitching in the lowest major league offensive environment since 1981. He also pitches in the National League (and thus faces pitchers), and also pitches in a pitcher-friendly ballpark half of the time. It’s a perfect storm of skewing raw numbers in his favor. ERA and FIP both have the same fundamental flaw of meaning different things in different times and places. Unadjusted, they’re really only good for comparing two players on the same team at the same time. The author is correct in noting that Kerhsaw’s ERA and FIP are really, really good, but does so in a way that fails to take context into account.

There is a better way to gauge Kershaw’s impact historically (on a rate basis), while still appreciating his brilliance. ERA- and FIP- adjust for park and league, so they’re great ways to look back at previous seasons to compare numbers. Values of 100 for both are average, and a point lower than 100 means a percentage better than league average. Right now, Kershaw has an ERA- of 48 and a FIP- of 52. That means that his ERA is 52% better than league average and his FIP is 48% better than league average.

Where do those numbers rank historically? Since the season is almost over, let’s use ERA- and FIP- values of 55 as a barrier, knowing that Kershaw could fall below that number in his last two starts. Since 1920 (the end of the dead-ball era) there have been 7074 seasons in which a starter has qualified for the ERA title. Including 2014, a pitcher has only had either an ERA- or FIP- of 55 or below on 61 different occasions. That’s already the top 0.8% of pitcher seasons. The only other pitcher to make this list in 2014 is Chris Sale, who currently has a 55 ERA- but a 66 FIP-.

Of course, one thing that makes Kershaw’s 2014 amazing is that he has done well in both categories. By requiring both ERA- and FIP- to be 55 or under, that cuts the list down to twelve seasons. Twelve out of 7074 is 0.17 percent. On a rate basis, these qualifiers would make Kershaw’s 2014 better than at least 99.8% of other pitching seasons.

The other names on the list should be pretty familiar, too:

Season	Pitcher	ERA-	FIP-
1990	Roger Clemens	47	53
1994	Greg Maddux	37	55
1995	Greg Maddux	39	53
1995	Randy Johnson	52	45
1997	Roger Clemens	45	50
1999	Pedro Martinez	42	30
2000	Pedro Martinez	35	46
2001	Randy Johnson	55	46
2002	Pedro Martinez	50	51
2003	Pedro Martinez	48	49
2009	Zack Greinke	48	53
2014	Clayton Kershaw	48	52

Greg Maddux shows up on the list twice, and he’s in the hall of fame. Roger Clemens was the first to do it, adding a second time in 1997, and he should be in the hall of fame. Randy Johnson also did it twice, and he should be going into the hall of fame next year. Pedro Martinez did it four times, including his absurdly good 1999 and 2000 seasons (which Kershaw is not close to) and he’ll likely be entering Cooperstown next to Johnson.

The most recent name might surprise people. Zack Greinke’s 2009 season is frequently forgotten, likely because he played in Kansas City and his raw unadjusted numbers weren’t memorable. But that season was every bit as good as what Kershaw is doing right now, with over 40 more innings pitched.

Again, these numbers are rate statistics, so they ignore innings pitched. Thus, they don’t account for the time Kershaw missed with his injury and also that pitchers don’t throw as many innings as they did in the past. That’s one reason why earlier seasons don’t show up on the list; more innings mean more time for outlier performances to regress to their means.

Even so, Kershaw is in some truly elite company. Four hall of famers and a teammate. That’s enough to sit back and watch history unfold. Let’s just be honest about what that history actually is.