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Robert Gsellman has been very effective for the Mets thus far

Gsellman is getting batters to make weak contact and thriving.

Arizona Diamondbacks v New York Mets

When the Mets announced their roster at the beginning of the season, it was at least a little bit surprising that Robert Gsellman had made the cut. While his very bad 2020 season consisted of just 14.0 innings of work, the 27-year-old had compiled a 5.03 ERA from 2017 through 2020, a significant step back from the promise he showed in 2016.

Despite the fact that Gsellman had options and could have been sent to the minors to start the year, the Mets felt he was their best choice for one of their eight bullpen spots. And so far, that decision has looked rather good, as Gsellman has thrown 22.1 innings in relief with a 2.42 ERA and 3.40 FIP. And he’s thrown more two or more innings in six of his thirteen appearances at a time that they Mets have been patching things together and absolutely need effective multiple-inning relievers on their roster.

When a pitcher is putting up significantly better numbers than he did in the recent past, you might expect to see some drastic changes in strikeouts or velocity. But Gsellman has struck out 15.4 percent of opposing hitters this year, which is a very low rate relative to the league average and below his own career rate, and averaging 94.11 miles per hour on his sinker, per Brooks, which is up slightly from last year but right in line with his career norms.

On top of that, Gsellman’s spin rate is down on his sinker, slider, and four-seam fastball compared to his past work. The spin rate on his changeup is up slightly compared to last year, which might have something to do with the fact that—as Steve Gelbs reported during a broadcast recently—he ditched the changeup that he had taught to Marcus Stroman and went back to one he was throwing previously. Even so, it’s still the second-lowest single season spin rate on that pitch since 2017.

Despite all of those flashy stats not jumping off the page, Gsellman has been elite in limiting hard contact. His 24.6 percent hard hit rate and 83.9 mile per hour average exit velocity both rank among the very best in the game—they’re in the 98th percentile in baseball, per Statcast. His changeup has been the star of the show when it comes to soft contact, as opposing batters have just a 10 percent hard hit rate and a .154 SLG against the pitch.

It is worth noting that Gsellman has ditched his curveball and is throwing his slider a bit less often than he did over the past two years, per Brooks Baseball. He’s thrown his changeup 18.62 percent of the time—exactly as often as his slider and something that’s never been the case for him in the past. Considering the success the pitch has had thus far, that alteration to his repertoire seems to have been a good decision.

In addition inducing weak contact, Gsellman has gotten ground balls on 50.7 percent of balls put in play against him, also per Statcast, which isn’t a career high for him but is a significant increase over his rate in 2019 and 2020. Combine all of that with the Mets’ drastically improved defensive positioning and defensive play in general, and Gsellman’s massive drop to a .246 batting average on balls in play is a reasonable conclusion, not a major cause for concern. He might not keep that number quite that low over the course of a full season, but it wouldn’t be surprising if it wound up being a good bit lower than his the .304 BABIP he has for his career.

Relievers are weird, and any outcome—from things blowing up entirely to Gsellman putting together a full season with a sub-3.00 ERA—could be considered unsurprising. But at least for now, Gsellman’s performance has been vital to the Mets’ success.