The Year of the Relief Cutter

Possibly the most infamous pitch from a single player in the history of the league is a cutter. Possibly the most infamous pitch from an active single player is a cutter. You can probably guess who those two players are, but, if not, they’re Mariano Rivera and Kenley Jansen. This is not a suggestion that these are the two best pitches of all time, as that is impossible to award. The combination of their extreme effectiveness and extreme usage has garnered the notoriety of the pitches. We are talking about inarguably the best closer of all time and arguably the best closer currently in the MLB, aside from maybe Craig Kimbrel.

Jansen’s and Rivera’s success derives almost wholly off one pitch. The pair rank 1st and 3rd in cutter usage in league history, respectively, although we only have pitch data on the latter half of Rivera’s career. Jansen has thrown it 81.3% of the time and Rivera 72.6% of the time, with Bryan Shaw sandwiched between the two at 73.5%. Of relievers who have thrown the pitch at least 20% of the time of their career, Rivera ranks 3rd and Jansen ranks 4th in standardized pitch value. Again, this does not include Rivera numbers until post-2006. When players as good as these two both thrive off the same singular pitch, it may suggest something about the pitch. In 2017, relief pitchers decided to embrace the cutter.

Now, not everyone went full Jansen and Rivera. But here are some cutter usage numbers from the five years prior to 2017, with the number of relievers who threw at least 100 cutters and the rate of cutters per fastball:

Year	# of 100 Thrown	Cutter/FB
2016	34	7.54%
2015	33	7.00%
2014	31	7.55%
2013	30	7.01%
2012	27	6.14%
Average	31	7.05%

This past season, those numbers exploded to 47 relievers and an 8.58% rate of cutters for every fastball. Where is this cutter revolution coming from?

First, the uniqueness of cutters needs to be established. They are classified as “cut fastballs,” but they are not necessarily always fastballs. They can be fastballs, but they can also be a sort of harder half-slider, and most pitchers have a few ticks off their cutter in comparison to their four-seam. Here is a fastball cutter, thrown by Jansen:

And here is the half-slider cutter, thrown by Wade Davis:

It can be difficult to compare cutters because there are so many variations of the pitch, but cut fastball or half-slider, there are some clear advantages to the pitch.

Sinkers are dying in the fly-ball-revolution climate. It’s a low-spin-rate pitch sinking right into the upward barrels of hitters, and the pitch is suffering. Cutters have the highest spin rate of any fastball, rivaling the rate of breaking balls. Spin causes the ball to stay up and resist its natural movement. You can see it in Jansen’s cutter. There is no exaggerated movement, but the ball seems to have an unnatural path. The pitch appears to “cut” through the air, as the name suggests, staying on one path from release to the plate. It’s difficult to judge the pitch, as it moves unlike a fastball but does not break, all while maintaining the velocity of a fastball. The unique path of the cut fastball allows it to be thrown in the strike zone while also generating whiffs.

The advantages of the half-slider cutter are more obvious. The cutter we see with Davis holds near typical fastball velocity, but also has tight and late movement. With lesser break than the typical slider, the pitch can be established in the strike zone, but the combination of velocity and break makes it difficult to contact. The velocity and subtle movement make it harder to recognize than a slider.

The nature of the cutter’s movement combats the upswinging of the current MLB. The pitch has such a unique combination of in-between velocity and movement that makes it difficult to read and just as hard to contact. It dominates other fastball types in spin, whiffs, and damage on contact, but still can be thrown in the strike zone just the same. Hitters cannot lay off the pitch but also cannot make consistent contact because of its uniqueness.

There was not the same explosion in usage with starting pitchers, though. I’m not sure of the reasoning, but possibly because relievers are generally more whiff-seeking and we are living in a whiffing environment. Whatever explanations there are, it’s obvious that relievers loved the cutter in 2017.