Sell Arizona Diamondbacks SP Patrick Corbin Right Now

Did you really think that 1.44 ERA and 0.98 WHIP would be sustainable? Not even close.

The MLB doesn't really have a Most Improved Player Award in the vain of the NBA or the NFL, but let's make one up for giggles. I'll call it the Jose Bautista Special for inexplicable jumps in overall stats from one season to the next.

Patrick Corbin would have to be this year's leader for the JBS this season, right? He finished last year at 6-8 with a 4.54 ERA in 22 games pitched (17 starts), hurt by a 1.327 WHIP. He's already topped that win total by May 21, and he's allowed less than 20 percent of last year's runs in over half the innings.

Sitting at 7-0 with a 1.44 ERA and a 0.979 WHIP, it's not only safe to say that Corbin's on fire: he's pitching like a Level 100 Moltres at this point. But will he keep it up, and is it worth selling high on him heading into the future? The stats say to bail while you can.

Luck on Balls in Play

There are three ways a pitcher can succeed, and all three have varying levels of how sustainable they are moving forward.

  • First, they can simply strike a bunch of guys out and not allow that many walks. This is the most foolproof method of determining a pitcher's worth: strikeout and walk rates are mostly on the guy chucking the ball.
  • Second, they can not allow that many homeruns. While this is somewhat on the pitcher, there is a small element of luck involved as well, especially in terms of matchups or the ballpark they are pitching at.
  • Third, they can allow a ton of balls in play, but their defense bails them out. This is obviously the least sustainable - what happens if you have a league-average defense instead?

It's probably not a good thing for Corbin, then, that the first way is out. His 21.2 percent strikeout rate is over the 19.8 percent league average, but it's not far enough ahead to be considered a legitimate strength. His 7.5 percent walk rate is just 0.5 percent under the MLB average and is actually two percent higher than his rookie numbers. His dominance doesn't come from making guys miss.

The homerun rate is certainly a factor here, but it's also a number that is wholly unsustainable. Two homeruns allowed over 62.1 IP? Please. That gives Corbin the third-lowest homerun rate among all qualified pitchers, only behind Doug Fister and Clay Buchholz. He may not reach the levels of the 2.7 percent MLB average or his 3.1 percent 2012 rate, but that number's bound to increase due to regression to the mean.

If I was a Patrick Corbin fantasy owner, though, it would be the third way that would scare me the most. His current .246 batting average on balls in play (BABIP) isn't just unsustainable; it's a downright statistical anomaly at this point in the season.

There is typically a high correlation between a high BABIP and the percentage of balls in play a pitcher allows that are line drives. It makes sense, right? Harder hit balls are typically more likely to find holes than slow dribblers. That's why, of the lowest 20 BABIPs allowed by qualified starting pitchers, only five hold a line drive percentage above the 21 percent major league average.

Some have reasonable explanations for their low BABIPs. Gio Gonzalez (24 percent LD%, .248 BABIP) and Matt Cain (25%, .242) have accomplished this feat for years through masterful use of other pitchers. Others, such as Jeff Locke (22%, .230) and Mike Minor (23%, .242), seem to be complete outliers.

Corbin falls in the latter category. He allowed 23 percent of balls in play as line drives last season, and as expected, his BABIP was a bit above the .294 MLB average at .319. This season, however, he has allowed line drives on an increased 24 percent of his balls in play... and his .246 BABIP ranks 16th among qualified major league pitchers. That doesn't make much sense.

By this point, it should be obvious we don't think that's going to continue. We have Corbin with a 1.35 WHIP the rest of the way. It's not the walks' fault; we actually have that static at 7.5 percent the rest of the season. Those hits, though, are bound to increase over time, way up from his current 6.2 hits allowed per nine innings that ranks ninth among qualified hitters.

Looking Forward

This is normally the part where I say, "Oh, but despite all that, regression to the mean shouldn't hit him that hard, and he'll be moderately fine the rest of the way!" Normally, I'm a comforting voice in the wind, assuring you that you have done the right thing holding onto this player you revere so dearly.

Today is not that day. I don't like to be the one calling out for the iceberg, but...

Projected Rest of Season Stats


See that last column? We project Corbin to pitch 0.78 runs per nine innings worse than the league-average pitcher. So much for the Jose Bautista Special.

Granted, even these stats the rest of the way would give him 13 wins, a 3.18 ERA, and 133 total strikeouts this season. But what has already happened doesn't help you much going forward. Given regression to the mean, his value will never be higher than it is right now. Get out while you still can.