Greg Weissert has inserted himself into the conversation for a high-leverage role through his performance this spring as well as his 2025 season. Aroldis Chapman and Garrett Whitlock stand uncontested as the primary options for the eighth and ninth inning spots, but a lack of additions in the bullpen this offseason has left the door open for Weissert to emerge as the other set-up man. His spring outings thus far turned heads, going two innings, striking out two and not giving up a hit in either outing.Â
Now, spring box score results are not worth spending much time on, as some fans might remember someone like Trayce Thompson dominating 2025 spring, hitting home runs seemingly every other at-bat, but not seeing any time with the big league club. For pitchers, looking at new movement profiles, new pitches, or an uptick (or decrease) in velocity can set the table for what to expect in the upcoming season.Â
Pitchers will often over-utilize pitches to get feel for them in game, so while keeping hitters off balance is a plus in the spring, it is rarely an omen for how the season will go. Still, at least from the initial data, it appears Weissert has improved his movement profile on his primary pitches.
Weissert’s strongest offering his is frisbee-like sweeper, which was put him on the map after the Red Sox as part of the Alex Verdugo deal. His sweeper’s -20.1 inches of horizontal break is the most among any qualified pitcher, moving 6.2 inches more than the average sweeper. As if it could get better, Weissert has shown up to Fort Myers, throwing a UFO sweeper with now 22.5 inches of horizontal movement. These two additional inches have moved the pitch from a 113 tjStuff+ to now a 118 mark, making it a pitch that moves 18% better than a league-average sweeper.
 
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One interesting note about the pitch is that he has made it his second offering after throwing it as his fourth-most used pitch last season. This could be some experimentation like I had mentioned previously or an indication of a slight change in approach. We can see thanks to the top right graphic that he used it primarily against righties, which makes sense for it’s use as a chase pitch. Just look at the swing Javier Baez tried to get off against it.
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Nasty. His primary pitch, as with most pitchers, is his fastball, which grades out as below average, mostly due to his low extension and below-average velocity (94.1). While his velocity has not improved thus far, the induced vertical break did, improving from 12.6 iVB to now 13.9, allowing it to stay up longer and fool hitters. To be fair, results wise, it was still a solid pitch last year, generating a minimal .296 xWOBA on contact and an above average 31 percent chase rate, but this tweak should make those results more sustainable.
Finally, his changeup has shown massive improvement this spring, going from a 101 tjStuff+ to now a 106 thanks to an extra inch of horizontal break and far more distinct vertical movement. The effectiveness of a changeup is its ability to pair with a fastball for as long as it can before it drops off the table, getting hitters to swing over it for a whiff or beating into the dirt.Â
His change was already effective at the latter, generating the second-highest groundball rate (82.4%) among pitchers who had thrown the pitch at least 75 times. It was not great at generating whiffs, though, sitting at only a 13.5 percent swinging strike rate. An additional inch downward won’t hurt his prospects on whiffs, but it likely still won’t be a big piece of his arsenal. An additional inch of horizontal run against lefties though, the side he would primarily throw it to, can and will create more problems. Here is perennial MVP candidate Corbin Carroll facing his 2025 changeup:
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Weissert shoved last year for one of the quieter sub-3.00 ERA reliever seasons in 2025, posting a 2.82 mark. Improvements in the pitch mix should only help to build on that and hopefully create a three-headed monster starting in the seventh inning. He is largely platoon-proof as well, as neither left-handed nor right-handed hitters managed even a .300 wOBA against him.
This Sox team is one that will thrive thanks to its defense and pitching. I expect plenty of close games in the seventh, and if Weissert can use this improved arsenal to set the table for Whitlock and Chapman, opposing teams are going to need to have a lead before they entered the final third of every game.