Jacob deGrom has some things to figure out. (USATSI)
Jacob deGrom has some things to figure out. (USATSI)

Mets pitcher Jacob deGrom hasn't been bad through his first five starts of the season, but he hasn't been quite as sharp as we expected after his Rookie of the Year campaign. Should Fantasy players looking for deGrom to be an ace be concerned about the dreaded sophomore slump?

First of all, we should determine if deGrom was an obvious regression candidate from his rookie season to now. The easiest way to do this is by looking at his FIP, in comparison to his ERA. Even a mediocre pitcher can string together 140 innings of sub-3.00 ERA if they have luck on their side, but it's harder to keep that up in the future if you don't have the right skills backing it up.

Fortunately, deGrom passed this test with flying colors as a rookie. His 2.69 ERA was stellar for a rookie, and he backed it up with a 2.67 FIP, indicating he didn't have much luck on his side. His .297 BABIP was close to league average, and even if his xFIP (which normalizes home run rate to league average) indicated he might have been a bit over his head, it's not like anyone would think much less of deGrom if he had a 3.03 ERA instead; that would have amounted to about six extra runs allowed over 140 innings.

Given his age and rookie-season peripherals, there wasn't much to suggest deGrom was a risk entering the season, though his injury history was a red flag. However, deGrom's velocity is up across the board, so an injury doesn't seem likely, which raises the question; why is he seemingly moving in the wrong direction? After nearly matching his ERA to his FIP last season, he has a 3.34 ERA and just 4.04 FIP so far. That isn't a great sign.

To be clear, this isn't necessarily a reaction to deGrom's consecutive subpar outings against the Yankees and Nationals. Everyone is allowed a few bad starts, so I'm not suggesting you should panic as deGrom owners. However, there are some concerning signs to point to.

Specifically, deGrom's strikeout rate has fallen from the ranks of the elite to the pedestrian. He has tumbled from 9.24 strikeouts per nine to 6.98, and his swinging strike rate has fallen from 11.7 percent to 9.2. And, it seems like the main culprit has been deGrom's fastball, which has gone from a weapon to something of a liability.

Despite his velocity remaining nearly identical, deGrom just doesn't seem to be fooling hitters quite the same way. He can still run his fastball up there consistently in the mid-90's, but he isn't garnering nearly as many swinging strikes with it. Opposing hitters swung throw 12.3 percent of his four-seam fastballs last season, including 27.2 percent of the ones they swung at. This season, those numbers have tumbled to 7.7 and 17.4 percent.

Underscoring the issues he has had fooling hitters with his fastball, deGrom's heater has been hit pretty hard as well. Last season, opposing batters managed just four home runs on 992 four-seamers (0.4 percent), with a .193 average and .102 Isolated slugging percentage. He has already surrendered three long balls with his four-seamer, on 246 offerings (1.2 percent), with a .189 average and .208 ISO.

There are two ways to look at his fastball troubles. You can look at it optimistically and say that, with no warning signs regarding his velocity, he should regress to his previously established level. And that is a perfectly reasonable response; we're talking about less than 30 innings, so there's no reason to panic. He could go out Wednesday night and run through the Orioles for 12 strikeouts, and it wouldn't surprise me at all.

The more pessimistic view would be to say that, despite his hard-throwing ways, deGrom was never much of a strikeout pitcher in the minors. He built his minor-league success on strong command, but never had a K/9 above 7.8, so some skepticism is deserved. It's hard to strikeout more than a batter per inning over 140 innings without ability, but that isn't a definitive sample size by any means. Especially when it stands out as an outlier for your career.

Looking at the heat maps for his fastball from BrooksBaseball.net, we can also see that deGrom is having a bit of trouble keeping the ball down in the strike zone. 

When he has missed, he has missed up, which might also explain why his groundball rate has fallen from 45.4 to 38.0 percent. Again, we're dealing with very small sample sizes here, so it's possible this trend corrects itself, but it is worth noting.

Because he was so good last season, deGrom has more than earned the benefit of the doubt. And it's not like he's been bad this season anyways. However, there are some early warning signs that he might be more of a mid-rotation starter, which isn't exactly what you were hoping for coming into the season.