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The Supremacy of Kenley Jansen

Almost a month into the season, Jansen has proved his worth—and then some—so far.

Photo by Maddie Malhotra/Boston Red Sox/Getty Images

When Kenley Jansen signed with the Red Sox in December, he lofted some pretty high praise on the organization:

Knowing that we’re going to Boston, it’s one of the historic organizations in baseball,” Jansen said. “Just immediately, the weight that the name ‘Red Sox’ carries gets you excited, gets your adrenaline going. You know this is a historic organization. It’s all about winning here. It definitely gives me even more focus to continue, to get back in that weight room, work hard, and try to be a better player next year.

I don’t know if fans had the same excitement towards Jansen. A 35-year-old who had only ever pitched in the National League — did he have anything left in the tank after a dominant season with the Braves? Why did Atlanta trade for Raisel Iglesias instead of sticking with Jansen? With other free agents like Edwin Diaz (though he did quickly re-sign with the Mets) or tantalizing trade rumors for David Bednar, could Jansen replicate even a modicum of the success that made him the NL leader in saves last season?

One month into the 2023 season, it’s safe to say he’s been the most consistent addition to the bullpen and the closer the Red Sox have been dying for the last three seasons.

So far this season, Jansen has made eight outings. The Red Sox have won every single one of those games he’s taken the bump. 5-for-5 in save opportunities, with one win and one hold, he’s shown both dominance and resilience, depending on which outing you look at.

Take his Red Sox debut, the second game of the season on April 2nd against Baltimore. A quick first two outs, striking out Ryan Mountcastle and eliciting a one-pitch groundout to Anthony Santander. Despite a bloop single by Austin Hays, a stolen base, and a walk to Gunnar Henderson, he came back to whiff Jorge Mateo and gave Boston of a chance down one going into the bottom of the 9th inning. We all know what happened next.

How about April 14th against the Angels? Up two runs and facing the absolute meat of the Halos’ lineup, he strikes out Mike Trout, Shohei Ohtani, AND Hunter Renfroe to seal a save and a victory.

Friday against a red-hot Brewers team with a one-run lead? 1-2-3 in the 9th, with two more K’s to finish the game off.

Last night? He saved Kaleb Ort’s bacon when Jansen shouldn’t have even lifted a finger to come in and get two clean outs.

If you want to look under the hood, there’s a big reason Jansen has been so effective his season. The pitch he uses most often at 79.4% of the time, Jansen’s cutter, is otherworldly.

Baseball Savant’s descriptive measures and 2023 Percentile Rankings for Kenley Jansen as of 4/25/2023.
Kenley Jansen has been dominant this season.
Baseball Savant

His cutter, no matter what, is well above league average by an astronomic factor. The spin he puts on it is almost the best in the league. It has an xBA of .110 and an xwOBa of .136. It has a whiff percentage of 37.7% and a putaway percentage of 38.5%—the number reflective of how often it is thrown in a two-strike count resulting in a strikeout. It’s even more deadly when it’s set up by a slider 10 MPH slower, at a 50% whiff rate, with the same vertical drop as his cutter but even more horizontal spin. It’s hard to be a practically two-pitch pitcher in this era of baseball—yes, I’m ignoring his pseudo sinker/fastball that’s used the least and isn’t as effective—but Jansen is proving to be not just potent, but dominant with his arsenal so far.

The most important stat that I’ve left out so far, but I hope can be surmised by now? A 0.00 ERA. No runs allowed.

Imagine this season how someone like Matt Barnes, Hansel Robles, or Jake Diekman would have fared in any of these situations. Over the last two years, we’ve seen countless instances of games given away because of either careless pitching or a lack of effectiveness by any of the closer-by-committee candidates Alex Cora has had to call on.

I said a month ago in OTM’s season predictions that Kenley Jansen would be the most important player. The Sox could have two, possibly three more losses already this season if he didn’t maintain his composure and pitch like a true closer. In my mind, those three instances are the second game of the season against the Orioles, the weird Verdugo walk-off against the Twins where Jansen kept it tied in the 9th, and a game on April 9th in Detroit where Jansen gave up two hits but kept his composure to save the game unscathed.

The difference between 13-12 and 10-15 this season is the difference between knocking on the door of the third Wild Card spot and sitting closer to being one of the worse teams in the AL. Does it make a difference now only 15% into the season? Maybe not. However, every win will matter down the stretch. When you get to September baseball, it’s almost instinctive to look back on April and May and go, “If only we won these games, then we wouldn’t be in this position.” Jansen has made sure he isn’t a reason they’re losing early on. Only time will tell if it makes a difference after 162 games.

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