Am I gonna regress from a 1.95 era? Most likely check anyone's stats lol some people are idiots. Is it spring training yet— Jarred Cosart (@JarredCosart) January 29, 2014
Jarred Cosart is a 23-year-old right-handed starting pitcher who made his major league debut with the Astros last season, having come over from the Phillies organization in the July 2011 Hunter Pence deal. It's understating things to say that he did quite well. Cosart allowed just 13 earned runs in 10 starts comprising 60 innings.
In one sense, Cosart is right to imply that it's redundant to ask if he's going to regress. After all, no one is consistent at that level. Christy Mathewson wasn't with a lot more conditions in his favor than Cosart has, and ditto Bob Gibson. Closer to our own time, Pedro Martinez and Greg Maddux posted two sub-2.00 ERAs apiece, but they weren't able to maintain that level of efficiency for very long either. Maddux did it for two seasons in a row (from 1994-1995 he went 35-8 with a 1.60 ERA in 411.2 innings),
The thing is, that's not what people are talking about if they're talking about Cosart's ERA being about to rise. You knew that Maddux and Martinez's ERA was going to rise, but you also knew that their overall level of performance, as indicated by things like strikeouts, walks, and home runs allowed, was such that it might rise to 2.50. With Cosart, the question isn't whether his ERA will be 1.95 or 2.50; if his ability to find the strike zone and miss bats remains the same, it's whether it will be 4.00 or 5.50.
Cosart is a strong prospect who could be very good next year. His fastball averaged 94.5 miles per hour in the majors, and he showed a real penchant for inducing ground balls: his 1.2 ground-ball/fly-ball rate would have been more or less tied for third in the majors had he pitched enough innings to qualify, behind only Justin Masterson (1.5) and A.J. Burnett (1.4) and roughly even with Doug Fister and Rick Porcello. As you know, it's very tough for batters to chain up a sequence of hits that lead to runs when they're hitting that many balls on the ground, and in the whole history of baseball no one has yet hit a home run on a grounder to shortstop.
Cosart walked 5.3 batters per nine innings during his stint in the majors -- the National League average for a starting pitcher was 2.8 -- and struck out 5.0 against a league average of 7.2. We know that when a pitcher lets batters make contact at an above-average rate, bad things happen. A strikeout has a very limited range of outcomes and overwhelmingly results in the batter dragging his bat back to the dugout. Put wood on a pitch and a ball might find its way to a fielder's glove, but then again it might not. As such, that low strikeout rate, combined with the baserunners from the free passes he issued, should have meant trouble for Cosart. The average batter hit .297 on balls in play (BABIP) last year.
For Cosart, that number was .246.
A small number of pitchers exert some measure of control over their BABIP, but the vast majority of them tend to circle around the league-average figure, with fluctuations being due more to the changing natures of the defense around them and the vagaries of luck. But just as no pitcher is consistent at a 1.95 ERA, no pitcher is consistent at a sub-.250 BABIP. There have been 147 pitchers who have thrown at least 1,000 innings this century. The top-10 for lowest BABIP starts with Matt Cain at .268 and rises quickly, with less than half maintaining better-than-average results across that span. Just 32 pitchers had seasons of below-.250 BABIPs (162-inning minimum), and nearly all of them experienced at least some rise in subsequent seasons (see table).
While it is facile to look at every pitcher who had a strong season due to a low BABIP and automatically forecast a disappointing encore, skepticism is not unreasonable. Note the list contains both some of the all-time greats as well as some obvious one-hit wonders... And a lot of Barry Zito, which says... Well, something about the universe being cruelly deceptive sometimes.
Cosart was a far better pitcher in the minors last year than he was in the majors, even if the results weren't as good. If you add up his 2012 and 2013 work at Double- and Triple-A you get 207.2 innings, 183 hits allowed 101 walks, 185 strikeouts, and an ERA of 3.29. The 4.4 walks per nine innings is problematic -- only three major league pitchers passed more than 3.9 batters per nine last year -- but in contrast to Cosart's major league work he was able to offset them to some degree with 8.0 strikeouts per nine. Between the ground balls and the minor league strikeouts, there is reason to have hope for Cosart's continued development despite the depressing walk and strikeout ratios in the bigs.
Cosart said in a subsequent tweet that, "people get technical on [Twitter] so obviously anything above a 1.95 is regression to them." It is to be hoped that Cosart's followers aren't so stupidly literal-minded; if anyone were to insist that it's 1.95 or Cosart is a disappointment, that would be unrealistic indeed. One suspects, though, that they're looking first at what his rates suggest and then inferring a catastrophic fall -- which, whether Cosart likes it or not, is a realistic thing to do. The concern isn't that his ERA will rise from 1.95; that's a given. It's just how far it will rise that is provoking cries of "regression" rather than unrealistic expectations.