Michael Fulmer opened the season as the Tigers’ top prospect. After just 15.1 innings over three Triple-A starts, the Tigers couldn’t wait any longer, recalling him to debut at the end of April. And boy what a decision that was, as Fulmer now owns a sparkling 2.11 ERA after yesterday’s start in 13 games.

A deeper look, however, suggests the happy days aren’t going to last a whole lot longer. You see, heading into yesterday’s game, he owned the third largest gap between his ERA and SIERA, and that gap most certainly widened given his mediocre peripherals, but just one earned run allowed, in yesterday’s start.

His BABIP now sits at a suppressed .252, which is quite an accomplishment considering the Tigers defense has posted a UZR/150 of -8.2, which ranks second worst in baseball. So Fulmer has either gotten the best fielding work from his team that they are capable of, been the recipient of extremely good fortune, or has managed to induce batters to hit balls where his defenders are. Or perhaps a combination of all three.

The interesting thing is that his entire batted ball profile is essentially league average. Well, except for a couple of extra grounders at the expense of fly balls, which if anything, should increase his BABIP, not lower it. There is one big difference though — his IFFB%. The league average starter has generated pop-ups at a 9.3% clip. Fulmer is at a lowly 5.1% rate. A high pop-up rate would have been one explanation for the suppressed BABIP, but instead his mark would typically be an explanation for a high mark. So there is seemingly nothing you could point to statistically to make the argument that Fulmer is deserving of a low BABIP. Given the porous Tigers defense, it’s likely to shoot up in a hurry.

Then we have the issue of his LOB%. Heading into yesterday’s start, he had posted the third highest mark among all starters with at least 50 innings pitched. Oftentimes you see a high LOB% paired with a suppressed BABIP or HR/FB rate, so once the BABIP regresses toward the league average, his LOB% is going to plummet and the runs will start piling up.

Next is the problem of his innings total. He threw about 125 innings last year and at 76.2 innings so far this year, is unlikely to start a full slate of second half games like an established 200 innings starter would. He’s likely to get a start skipped here and there or be shut down a week or two early, if not both.

I’m not expecting a collapse. Although his slider has been barely above average from a SwStk% perspective, both his four-seamer and changeup have been excellent at inducing whiffs and grounders. His stuff has been there and one might assume would continue to result in strikeouts, but you never know when hitters will adjust to a rookie hurler. So while I’m not screaming SELL SELL SELL because I think he’ll “earn” negative value, there’s real risk that he’s close to replacement level in 12-team mixed leagues the rest of the way. Given his top prospect status, high strikeout rate, and microscopic ERA, he’s the perfect candidate to dangle for an upgrade.