David Peterson is not maximizing his repertoire

Given the reigns as a full-time member of the Mets rotation with Jose Quintana out, David Peterson has had an uneven beginning to his season. Mets fans certainly shouldn’t be shocked to see Peterson’s inconsistencies so far; this is who he has always been. His problems through his first two starts have been exactly the types of issues he has had that have made him so frustrating to watch in his career so far: deep counts, lots of baserunners, and not enough strikes.

But what also makes Peterson so maddening is that there’s reason to believe he can be better than this. The former first round pick has upside beyond what he has accomplished so far, and most of it comes from his slider. Believe it or not, Peterson’s slider was one of the most effective pitches in baseball last year.

The whiff rate on Peterson’s slider in 2022, 47.9%, ranked 10th-best among all pitches thrown in baseball (min. 100 PA) according to Baseball Savant. For context, that ranks above Corbin Burnes’s curveball, and is within shouting distance of Edwin Diaz’s slider (54.7%) and Shohei Ohtani’s splitter (49.4%). The pitch also registered a PutAway%—the rate of two-strike pitches that resulted in a strikeout—of 32.9%, which was the sixth-highest in baseball among the same sample size, and it happened to rank one spot above Jacob deGrom’s fastball.

When hitters made contact with Peterson’s slider last year, they didn’t really do much with it. The pitch had a .175 batting average against and opponents slugged just .292 SLG off of it. That, combined with his changeup (.194 BA against in 2022), gives him a good base to miss bats and get hitters out consistently.

But here’s the problem: his fastballs get absolutely killed. Last year, hitters batted .280 off Peterson’s four-seam fastball with a .427 SLG%, and hit .333 off his sinker with a .590 SLG%, while only whiffing 15.4% of the time against that pitch. He threw either iteration of his fastball over 49% of the time last year, while his slider was thrown 29% of the time and his changeup only 16% of the time. That slider usage was actually up from previous years, when it was more around 25% in 2020 and 2021.

Through his first two starts this year, Peterson has not only continued to throw his fastballs more than any other pitch, but he’s leaned on it even more. He’s thrown his two fastballs for exactly 50% of his pitches, while only throwing his slider only 23.9% of the time, though he’s upped his changeup usage to 21.6%. This was particularly noticeable in his start on Wednesday, as he had no command of his fastball all game and kept losing it arm-side, but still kept trying to throw it anyway. He threw his slider only 12 times, and got two of his five strikeouts on the pitch. Now, his changeup was getting good results for him in that game, and he threw that more than usual, but he still wound up throwing his four-seamer for 48 of his 92 pitches despite not being able to locate it at all. Needless to say, it didn’t really work out for him.

The idea of “just throw your best pitch the most!” seems like an overly simple one, especially when coming from a blogger with no pitching, scouting, or professional experience. However, don’t take it from me, take it from some of the smartest teams in baseball; the “spam your best pitch” strategy is actually what a lot of modern pitching development is based around. A lot of teams these days will specifically look for pitchers with good characteristics on certain pitches, and tell them to throw those the most and ditch the pitches that aren’t getting results.

There are numerous examples of this across the league among both relievers and starters. Kyle Wright, for one, was struggling to stick in the big leagues before 2022, but then the Braves had him up his curveball usage to a career high 34% last year—more than double where it was previously—and it helped turn him into a top of the rotation pitcher. Andrés Muñoz became an elite reliever once the Mariners plucked him off the scrap heap and told him throw his slider almost 65% of the time. A lot of Shohei Ohtani’s success as a pitcher comes from throwing his unhittable sweeper almost 40% of the time. Logan Webb, a good comp for Peterson, threw his slider and changeup a combined 69% of the time last year, and only threw his sinker the other 31% of the time. Hitters batted .327 against his sinkers, and only a combined .203 against the other two pitches.

The best example of what can happen when you maximize a pitcher’s repertoire, though, might be Dylan Cease. Before 2022, Cease had a similar pitch distribution to Peterson, throwing his fastball nearly half the time and his slider only around 30% of the time, even though the slider had extremely good characteristics. In 2022, he basically flipped the usage of those and threw the slider 43% of the time and the fastball only 39.8% of the time, and, probably not coincidentally, Cease turned from an erratic fourth starter into a staff ace for the White Sox last year.

Now, that’s not to say Peterson will become an ace like Cease if he throws his slider more. Cease’s fastball is still far better than Peterson’s, and so is his control. But if Peterson is having this much success with his slider, trends around the league indicate he should probably try to squeeze that for all its worth. Because of injuries, the Mets are now relying on David Peterson to be a dependable member of the rotation this year. If he’s going to be that, he has to start by actually throwing the pitches that hitters don’t square up. Otherwise, he may never tap into his full upside as a starter.