Should Martín Pérez get back to throwing his sinker more?

Martín Pérez has been pitching at the highest level for 10 seasons now, and as is usually the case with pitchers who log that much playing time his approach on the mound has changed throughout the years. After all, reinvention and constant adjustment is part of the game. Batters adjust their stances and tweak their swings, while pitchers update their mechanics and try to improve their spin rates.

For Pérez, he made a relatively significant adjustment in 2019 by introducing a cutter to his repertoire. The pitch joined the ranks of his fastball, sinker, changeup and curveball that year and immediately became his most utilized pitch, a trend that carried through 2020 and and has continued this season as well. This year alone, he has thrown his cutter 34 percent of the time (per Baseball Savant), which outpaces all his other offerings, as his changeup comes in second at a 23.8 percent usage rate.

The sudden introduction of the cutter and the immediate reliance on it came at the expense of Pérez’s sinker, which was his go-to pitch for years. From 2014 to 2018, he always threw his sinker at least 35 percent of the time, reaching a peak of 50.6 percent in 2018. During that same timeframe, Pérez never threw another pitch at a 30 percent clip. However, once he brought the cutter on board, his sinker got relegated to a secondary role, falling to third in the pecking order in terms of Pérez’s most used pitches in 2020.

During the 2019 and 2020 seasons, the move to the cutter paid off. In both seasons, opposing hitters produced a wOBA below .300 against the pitch, while the rest of Pérez’s offerings, except for his 2019 changeup, yielded marks of .300 or higher. In addition, during the first year he began throwing it, Pérez actually had the second-most valuable cutter in baseball among qualified starting pitchers, according to FanGraphs, and just last year his cutter was the only pitch he threw with a positive value for the entire campaign using those same metrics from FanGraphs.

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As Pérez dazzled with his cutter, his sinker not only began to be used less often, but its effectiveness took a dive as well. After having one of the 10 best sinkers in baseball among qualified starters in 2016, according to FanGraphs, Pérez’s sinker yielded negative value in 2019 and 2020.

With all that pro-cutter evidence, it’s no surprise that Pérez has doubled down on his cutter usage this season, as that 34 percent mark I mentioned earlier puts him on pace for a career-high in terms of cutter utilization. Looking at his overall body of work, there’s not a ton of reason to expect him to go away from his current strategy either.

Pérez has been quietly humming along and, although he’s probably considered a back of the rotation arm, you could make the argument that he’s been performing more like a top of the rotation guy for the Red Sox this season. He is second among Red Sox starters with at least five starts in ERA+ and FIP and tied for second in that group in fWAR. He has been successful despite pretty mediocre velocity and spin due to his ability to avoid the barrel of the bat. According to Baseball Savant, he is in the 84th percentile in MLB in barrel rate, the 78th percentile in average exit velocity and the 70th percentile in hard hit rate.

Pérez spun his most flawless gem of the season in his last outing, shutting out the Los Angeles Angels over six innings of work. He has allowed one earned run or fewer while pitching through at least five innings in three of his last four starts. Again, the lower inning total may take some of the shine off of that production, but it’s still been a solid few weeks for the left-hander.

As all this has been happening, Pérez has been boosting his strikeout rate beyond his normal levels, with his 21.3 percent punchout percentage easily outpacing any of his previous season-long marks. This follows a trend that coincides perfectly with the dawn of his cutter, as Pérez has produced a strikeout rate of at least 17 percent in each of the last three seasons (including 2021) after never reaching 17 percent in the preceding seven years. And, as you might expect, in 2019 and 2020, Pérez had a higher strikeout rate with his cutter than any other pitch, according to Baseball Savant.

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But here’s where things get a bit more interesting. Despite all the benefits the cutter has brought for Pérez, it hasn’t been as great a pitch this season, even if it is his primary offering. With a plus-three run value and a .444 wOBA against, according to Baseball Savant, Pérez’s cutter has arguably been his worst pitch. It’s a curious development to be sure, but it’s only made that much more intriguing when you look at his sinker. His once favorite pitch has been his best one this season, yielding a run value of minus-five and a strikeout rate of 32.7 percent, according to Baseball Savant. His infrequently used fastball is the only other pitch with a higher strikeout rate, but the rest of his pitches are nowhere near his sinker in terms of run value, although his changeup has been a solid offspeed pitch, yielding an opponent wOBA of .223 as Pérez’s second-most thrown offering.

So what does this mean? Possibly nothing, but it might mean that it’s time for a comeback for the sinker as Pérez’s first option. Admittedly, his sinker hasn’t been as good as his changeup or curveball in creating softer contact, but it’s still been his best overall pitch. Perhaps throwing a few more of them instead of cutters could help Pérez build on his recent run of success.