Now, there's certainly arguments to be had about how he stacks up to other great closers like Aroldis Chapman and Craig Kimbrel, but that's not what's interesting right now. What's particularly fascinating about Jansen (beyond the pure domination, of course) is how he's most similar to the great Rivera, in the sense that he almost exclusively throws a cut fastball, and even though batters know it's coming, there's still not a thing they can do about it.
A quick look at the raw numbers verifies that. Over the last four seasons, Jansen has used his cutter 90.3 percent of the time, which is even more often than the 87.5 percent that Rivera used his own cutter during his final four seasons. While he's toyed with a sinker in the past and occasionally drops in a slider to keep hitters honest, Jansen's game plan boils down to "I'm throwing you a cutter, deal with it."
That's not a strategy that works for most pitchers, but by digging into the Statcast™ data, we can see what makes Jansen's cutter so elite. Immediately, a few things jump out. Among the 108 pitchers who have thrown the cutter at least 30 times, Jansen's is:
• 1st in average spin rate (2,610 rpm)
• 2nd in average extension (7.04 feet)
• 3rd in average perceived velocity (94.7 mph)
• 3rd in individual perceived velocity (99.26 mph to Wilin Rosario on May 17)
Now a lot of that sounds like Jansen is just blowing the ball past people, and there's certainly a large element of velocity at play here. But as we've discussed previously with Nathan Eovaldi, elite velocity doesn't always lead to success if it's lacking movement. And for Jansen, movement's not at all his issue, as you can see from the tailing action on this 98 mph cutter he put past Collin Cowgill last year:
Jansen gets an average of 9.58 inches of vertical movement on the cutter, and while that's "only" the fifth-best among cutters, two of those above him are fringy soft-tossers who survive in the big leagues only because they get that movement. The only pitcher in baseball who gets as much movement on his cutter and more velocity is Houston's Josh Fields, and while he's been very good himself -- 1.86 ERA, 1.14 FIP -- he doesn't get as many swings on the cutter, and therefore fewer whiffs.
Last year, Jansen completed a "hidden perfect game," retiring 27 straight hitters over several appearances. In the entire history of baseball, only Chapman and Kimbrel have higher career strikeout percentages (min. 250 innings pitched) than Jansen's 39.8 percent. This season, thanks to that high-spin cutter that batters just can't lay off and can't connect with, he's been better than ever. It's not often that you can be that good when hitters know what's coming. Then again, when what's coming is all but unhittable, it doesn't really matter.