More thoughts on Kenley Jansen’s recent issues

Kenley Jansen made his first appearance of the NLCS last night, in the sixth inning with a 14 run lead. The inning was designed to boost his confidence and to gauge how effective he will be in high-leverage situations going forward.

He looked… okay. His cutter velocity was in the 89-91 range, not the 86-90 range he has been in in the recent past. He also fired a few sharp-looking pitches, like this one:

Jansen retired the side in order, but the inning was not a resounding success, as he still looked pretty shaky with his command and two of the three outs were very loud. However, the announcers talking about how his cutter doesn’t cut anymore (while showing a slow-motion replay of a two-seamer) makes it seem worth diving a little deeper into how the pitch looks compared to the rest of his career.

In some ways, it’s more accurate to say that Jansen’s cutter is cutting more than ever. Here is Jansen’s horizontal cutter movement over the course of his career, grouped by month:

During Jansen’s October struggles this season, his cutter has had more horizontal movement than at any other point of his career. You can see hints of that in the video above. The issues become more apparent when looking at the vertical movement of the pitch:

Jansen’s cutter has significantly less vertical movement than it has had in the past, and it has been trending downwards in recent years. Obviously, these movement changes also correspond with a downward velocity trend, especially over recent months, but it also brings to mind what made the pitch so special in the past.

Jansen grips his cutter like a four-seamer, and for the early parts of his career, it almost moved like one. The rise on that cutter in the early parts of his career was unusual, and the run was lower than most cutters too. It was that little cut at the very end of the pitch that let him live up in the zone and why so many batters swung below it or popped it up. That’s how he could throw just one pitch. In 2019, even after a career of slow erosion of that vertical movement, Jansen still had more rise on his cutter than the next-highest right-hander who averaged over 90mph by a margin of over an inch. That margin is now gone.

However, as you can see on the video above, the cutter can still be effective. That particular pitch is pretty atypical of Jansen cutters though, in that it’s not located high. As Jansen loses his vertical movement, perhaps the cutter should be thrown lower more frequently, as batters will be fooled less by the pitch’s rise. The pitch still has less sink than a typical slider, but it now has action that evokes it.

Jansen’s ball-in-play results on cutters reflect that to some extent. xwOBA is a flawed stat for reasons that I won’t get into here, but it’s usable shorthand for batted ball quality. Below is a chart that shows what happens to Jansen’s cutters when put into play, broken down by pitch height (for context, the league-average wOBA for balls in play was .369 this season).

Interestingly, when Jansen’s low cutters were put into play in 2019, they produced weaker-hit batted balls than the high cutters for the first time since Statcast started tracking. That reversed this season, but there are sample size issues, only nine low pitches actually qualified. For what it’s worth, batters still swung and missed much more often at Jansen’s high cutters this season (35% whiffs per swing this season) than his low ones (18%), but many of his low cutters were intended to be thrown higher, so they might not be moving quite like he wants.

Interestingly, Jansen has been responding to his cutter having less vertical movement this season with throwing it just about as high as he ever has:

Given what happens on balls in play, and given the change in movement, this response might not be the correct one.

It’s not really fair to criticize Jansen for failing to adapt his approach. He only threw cutters 63% of the time this season, by far the lowest rate of his career. But it’s also fair to wonder if said cutter is all that special anymore, with the way the vertical movement and velocity have dipped. It just lacks the Kenley Jansen-ness that it used to have.

Beyond all of this, though, the main ingredient of Jansen’s recent struggles has been his lack of command. Any proposed change in approach doesn’t really address that. Jansen’s vertical release point did change last night (about an inch higher on average than the outing before), but it was still in line with where it has been during his recent struggles. Jansen probably isn’t going to re-invent his approach overnight in the postseason, but one has to wonder if he’ll have to further change how he pitches to be successful moving forward.