Robert Gsellman was disappointing

Much like the Mets in 2018, Robert Gsellman exploded out of the gate before being something between terrible and mediocre the rest of the way. The result was an unremarkable season of relief; 80 innings of 4.28 ERA ball, with a 3.95 FIP and a lackluster 7.88 K/9. This was a marked improvement over his dreadful 2017, but hardly the step forward that many hoped to see from a pitcher who was once ranked as the 17th best prospect baseball by Baseball Prospectus.

I took a look at Gsellman back in July, trying to understand what changed after he followed up a stellar April (1.80 ERA, 1.81 FIP, .251 wOBA) with three months of horrible relief pitching (ERA above 4.50). The conclusion there was an ambiguous one; Gsellman’s velocity and movement were mostly unchanged, his location was only slightly worse, but batters had simply stopped fishing for balls out of the zone and pounding anything in the strike zone. I also noted that Gsellman’s changeup had been a terrible pitch that he should abandon, and that he should try throwing more fourseam fastballs up in the zone.

Gsellman pitched another 25.2 innings after that analysis was published, and on the surface, nothing really changed. He ripped off a fantastic August - 1.54 ERA, .203 wOBA, 2.99 FIP - but that hot streak was driven almost entirely by a .188 BABIP. He followed that up with a horrific September, posting a 7.71 ERA and allowing a .380 wOBA. Further, his strikeout rate dipped close to 2017 levels, sitting below seven over the final two months of the season. In an era when relief pitchers are expected to come in and blow batters away, that’s simply not viable (unless your name is Brad Ziegler).

In terms of his approach, Gsellman was much the same over these final two months. He leaned on his sinker to an extreme degree, throwing it more than 60% of the time, and sprinkled in his slider at a rate in the low teens. He continued to tinker with his bad changeup as well, and the results were still bad Finally, his fourseam was mostly an afterthought.

Doing the same thing and expecting different results is the definition of insanity, and Gsellman didn’t adjust much of anything as his season went downhill after a hot start. From a statistical standpoint, the 25-year old right-hander looks like little more than a mediocre middle reliever. That’s a particularly frustrating conclusion, both because of his prospect pedigree and because he looks like he should be better; this, for instance, is an objectively great pitch:

Regardless, intermittently beautiful and/or nasty pitches does not a late-inning reliever make. Gsellman had a chance in 2018 to seize the closer’s role but fell flat, and the Mets can’t rely on him to throw high-leverage innings next season (Note: they will, but they shouldn’t). He’ll enter 2019 as a huge question mark, two years removed from his stellar 2016 debut and lofty ranking prior to the 2017 season. Hopefully he can make the necessary tweaks and re-discover some of that early success.