Kenley Jansen’s Other Pitch

Kenley Jansen is one of the best relievers in baseball. This season, in some ways, he has been better than ever, posting a career low xFIP and career high swinging strike rate. The rest of his peripherals are in line with his career averages. His ERA isn’t great, but you should never look at reliever ERAs. He’s tenth among relievers in strikeout rate, and eighth in K%-BB%. Most of you already know this.

One thing to note, though, is how Jansen’s pitching has evolved over the course of the season. Here is a breakdown of his pitch usage month-to-month throughout his career.


So far in July, Jansen is throwing his highest percentage of not-cutters in his career. He’s still throwing them 80% of the time, but about 16% of his pitches this month have been sliders. That high rate of slider usage is his highest since the middle of 2011. Some of that is small sample size, since Jansen has pitched just seven innings this month (remember when we were worried about his high workload?). However, even when looking at full season pitch usage, he’s throwing more sliders than he has in three years.

It’s still a small number, but it’s worth looking into. What is the “one pitch pitcher’s” other pitch? First of all, it’s fun when it’s working well:

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That pitch was against Dan Uggla, so it only partially counts, but the pitch has been great when he has used it. You can see pretty clearly what Jansen is trying to do with the pitch in this plot, courtesy of Baseball Savant:


Of the 45 sliders Jansen has thrown in 2014, only four have been in the upper 2/3 of the strike zone (five have missed off the plate and up as well). 36 of the pitches have either been in the lower 1/3 of the strike zone, low, or off the plate below the midpoint of the zone. Jansen’s average slider location is at its lowest position of his career. He’s throwing it with more sink (downward vertical break) than ever. Currently, Jansen’s slider averages about 2 inches of sink (compared to 9.5 inches upward movement for the cutter). 180 relievers have thrown at least 40 sliders this season; Jansen’s slider has the 13th highest sink among all of them.

The extra sink and lower location are working. Jansen is getting good results on the pitch. Ignoring the 11 sliders he threw in 2009, he has a career high whiff/swing rate on his slider, 45.16%. In each of the last three seasons, Jansen’s slider has had a higher whiff rate than his cutter (as has his two seamer, which is a topic for another post). Jansen’s slider whiff/swing rate is 35th among the same reliever group mentioned previously.

As a result, Jansen is getting a relatively disproportionate number of strikeouts on the pitch. Twelve of his 66 strikeouts have come on the pitch, the 18.2% rate much higher than the 6.8% overall pitch usage. 28 of Jansen’s sliders have been thrown with two strikes, and another 11 have come on 0-1 counts. He has only thrown the pitch three times while the batter is ahead in the count (curiously, two of those pitches were to Carlos Quentin, in separate sequences). It’s his secret out pitch.

To get a better picture of  what the above numbers mean, here an outcome breakdown of the 45 sliders thrown this season:

  • 11 balls
  • 3 called strikes
  • 10 fouls
  • 14 whiffs
  • 7 balls in play – 3 ground balls, 2 fly balls, 2 line drives – 2 hits, both singles, 5 outs

That’s really, really good. On a rate basis, Fangraphs grades Jansen’s slider as his best pitch this year. On a cumulative basis it’s still the cutter, of course. It’s hard to tell if the positive results are because he throws the other pitches so often. It’s hard to study, since Jansen is so unique. The high degree of sink might point away from the frequency and towards it just being a really good pitch on its own. If Jansen continues his current pattern of throwing the slider more, I suppose we’ll find out.

These numbers and figures were generated before Tuesday’s game, where Kenley Jansen threw two sliders in nineteen pitches (10.5%). One slider resulted in a whiff, one was left up and hit for a line drive single. It was the fifth slider in the upper 2/3 of the strike zone, but the damage was still limited.

About Daniel Brim

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Daniel Brim grew up in the Los Angeles area but doesn't live there anymore. He still watches the Dodgers and writes about them sometimes.