He’s not there yet, but the righty is returning to his 2021 form.
When Garrett Whitlock arrived in Boston, he caught everyone by surprise and became a key piece of the 2021 bullpen. After that, he struggled. He moved from the pen to the rotation and back to the pen, all while dealing with injuries. Healthy for the first time in several seasons, Whitlock is back in the bullpen and is starting to look like the pitcher who burst onto the scene as a Rule-5 Draft selection.
Among pitchers with 40 or more innings pitched (an admittedly arbitrary threshold), Whitlock is 17th in strikeout rate. He’s dominated against both sides of the plate, holding lefties to a .200 average, while righties are at .225.
A big reason for Whitlock’s resurgence is his fastball. He throws a sinker almost 50% of the time, although the shape allows it to operate more like a four-seam fastball. The swinging strike rate is the best of his career at 14.5%, and he’s in the zone often. He throws hard and with great extension. As long as he continues to locate, there’s no reason to believe the pitch will fall off as it did in 2023 and 2024.
His slider has become his primary offspeed pitch, and it’s been dominant. It has a low zone rate at 36.4%, but makes up for it with an insane 44.6% chase rate. When contact is made, it’s not solid. The ground ball rate is above 50%, while the hard hit rate is just over 20%. If that’s not enough percentages for you, the putaway rate is 30%, which ranks in the top 20 among relief pitchers.
If there’s one area to critique Whitlock, it’s his changeup. Against lefties, the pitch has been great. He’s getting hitters to expand the zone frequently, which contributes to a solid swinging strike rate. They’ve hit over .300 against it, but the expected average is much lower, suggesting some positive regression. The putaway rate is down, but the two-strike location looks fine, so there could be some sequencing issues hindering the performance.
His issue is facing righties. In 2021, he was able to use his changeup effectively against righties, which limited walks by giving him a third pitch with a high strike rate. This season, the strike rate against righties is down to 53%.
It’s not incredibly common to have a changeup that works against same-handed hitters, but Whitlock did at one point. Unfortunately, his 2025 changeup is slightly different. The current changeup sinks more, which isn’t necessarily a bad thing. What’s more of a problem is the velocity. In 2021, he killed spin and velocity incredibly well. Now, it’s a little bit closer to his fastball in terms of velocity, and righties are seeing it better. They haven’t whiffed as frequently and are making hard contact. The putaway rate is also down about 16% from its peak. Righties have already fouled off more two-strike changeups than they did in 2021. The velocity change might have something to do with that.
Whitlock has been good overall and has improved from the start of his season. 13 of his last 15 appearances for the Red Sox have been scoreless, and outside of a blowup appearance against the Angels, he didn’t allow a run in June. With some better batted ball luck and two-strike execution, Whitlock’s stat line could be among the best in the league come September.