Figuring Out Why the Red Sox Signed Justin Wilson

Last week, the Red Sox signed left-handed reliever Justin Wilson for one year and $2.25 million, along with incremental bonuses that could take the contract up to a nice, round $3 million if he finds his way into 60 games. Because, as Nick John noted at the time, Wilson’s recent work doesn’t exactly inspire confidence, let’s dig into what the Red Sox might have been thinking. In 2022, Wilson got into just five games before Tommy John surgery ended his season. He missed the entire 2023 season due to a lat injury that derailed his recovery in July. Wilson finally returned in 2024, getting into 60 games, but the results weren’t there. He ran a 5.59 ERA and a 4.73 WHIP, surrendering 10 homers over just 46 2/3 innings. Wilson is 37-year-old journeyman, and since the 2020 season, he’s got a combined 5.02 ERA over 130 appearances. He’s not a lefty specialist; he actually has better numbers against righties both in recent years and over the course of his career. The Red Sox have given every indication that they mean to compete for a title in 2025. It’s fair to ask what made them think that Wilson could help them toward that end.

The first thing to note is that Wilson was particularly unfortunate last season. Among pitchers who threw at least 750 pitches, his .338 BABIP put him in the 91st percentile. His .354 wOBA was 36 points higher than his .318 expected wOBA, and that gap put him in the 98th percentile. His 15.9% HR/FB also ranked in the 91st percentile. Now, some of that was luck and some of it had to do with the defense and the ballpark. That’s good news for Wilson. While Fenway is slightly more hitter-friendly than Great American Ball Park, that friendliness comes in a different fashion. Fenway yields many more doubles and triples, while Great American yields tons of home runs. Wilson is a fly ball pitcher, so dialing down the homers should help him more than most pitchers, as will pitching in front of one of the best defensive outfields in all of baseball.

To be clear, even if Wilson’s actual stats had matched his expected stats last season, he still wouldn’t have been fantastic. His .318 xwOBA only put him in the 36th percentile, mostly because he allowed way too much hard contact. If the Red Sox expected him to pitch the exact same in 2025, they wouldn’t have signed him. Let’s dive into why they might think they can get more out of him.

Wilson throws a four-seam fastball, a cutter, and a slider (he also threw a few splitters, but they were so infrequent that we’ll leave them out of this discussion). The four-seamer and the cutter have a ton of rise. That’s why Wilson is such a fly ball pitcher, and it’s also why he ran one of the highest popup rates in all of baseball last season. Popups are automatic outs; they’re every bit as good as strikeouts. Wilson ran a solid 24% strikeout rate, but altogether, nearly 39% of his plate appearances ended in either a strikeout or a popup, which put him in the 93rd percentile of all pitchers who threw at least 40 innings. He was literally one spot above Tarik Skubal – yes, the same Tarik Skubal who’s about to walk home with the AL Cy Young Award this week. That alone is inspiring, but it could be even better. Wilson threw the four-seamer just under half of the time and the cutter just under a quarter of the time, but here’s the thing: the cutter was much better. The four-seamer had a .454 wOBA, compared to .303 for the cutter. The cutter didn’t rack up as many whiffs, but batters hit it much softer, popped it up much more frequently, and chased it a huge 42% of the time. What were the Red Sox known for this season? Telling their pitchers to ditch their fastballs. You have to imagine that they’re going to empower Wilson to lean more on his best pitch.

I suspect that the Red Sox will tweak Wilson’s slider as well as his location. He ran an elite 33.8 chase rate this season, but he also threw his pitches inside the strike zone at a pretty high rate. If he were to elevate his fastball and cutter a bit more, he’d probably throw more balls, but he’d also earn a lot more chases, and the tradeoff would surely be worth it. However, just dialing down his fastball is an obvious move that very much lines up with what the Red Sox are preaching these days. Signing Wilson was a small part of what looks like it will be a very big offseason, but it’s encouraging to see the Red Sox executing a plan.