Since the debut of Matt Harvey in the middle of 2012, the Mets have had quality arms debut basically every year. Some have been top prospects, like Zack Wheeler and Steven Matz, and some have come out of obscurity, like Jacob deGrom. Robert Gsellman is closer to the latter than he is the former, hair notwithstanding.
The former 13th-round pick was a godsend for the Mets in 2016. With several of the Mets’ starting pitchers injured, Gsellman provided quality innings late in the season. In 44.2 innings (eight games, seven starts), he posted a 2.42 ERA (170 ERA+), a 2.63 FIP (64 FIP-), a 3.38 xFIP (82 xFIP-), and a 3.76 SIERA, all while dealing with a torn left labrum. He had a 22.7% strikeout rate and a 8.7% walk rate to go along with those numbers.
The numbers do not lie: He was excellent in his short stint with the big club in 2016, and way above the league average across the board. Looking at his FIP, xFIP, and SIERA results as well, he did not luck his way into these numbers; he legitimately pitched this well.
Despite this, there are some questions about Gsellman going into 2017. The quality of competition he faced and his lack of a third pitch are a little concerning.
In his seven starts, he faced the Nationals twice, the Braves twice, and the Phillies three times. While it is not his fault in any way, he faced two poor offenses in five of his seven starts. It is important to note that he surrendered just one run in 11.2 innings against the Nationals. It will be interesting to see how he fares against tougher teams, as well as when teams see him more often.
Gsellman has never been much of a strikeout pitcher; his 22.7% strikeout rate last year was his career high, minors included, since his 2013 season in Brooklyn. 22.7% is right around league average, and is certainly respectable, but it will be tough to maintain with only two pitches, as he did last season.
According to PITCHf/x Pitch Values (you can read more about that here), his best pitches were his four-seam fastball and his slider. All numbers are expressed as runs saved per 100 pitches.
Four-seam fastball (FA/C): 1.45
Two-seam fastball (FT/C): 0.45
Slider (SL/C): 2.31
His curveball was also effective, though he threw just 76 of them. If he wants to continue to strike people out at a career-high rate, he’ll most likely need to develop another effective pitch apart from the four-seamer and the slider. The slider has become a top-tier pitch, but a slider-fastball combination may only get him so far strikeout-wise. His curveball showed signs of being a good pitch, but as of last season he still needs to trust it more.
Despite these concerns, Gsellman legitimately was excellent in 2016. While he may not reach the heights of his last season numbers, he should still be a very good option in the back of the rotation in 2017.