Andrew Kittredge is throwing more four-seamers, and here is why it is working

Over the past few months, I have become obsessed with Andrew Kittredge. This obsession has prompted articles like this one, as well as tweets like this and this. After Tuesday night, when he threw a near immaculate inning en route to a two inning save against the Phillies, I felt the need to talk about him again, because I have noticed something different.

In Kittredge’s Tuesday night outing, he threw a total of 26 pitches. Of those 26 pitches, he threw 5 four-seam fastballs; just a shade below 20 percent. Pointing out pitch usage in a one game sample is tricky, but this is outside the norm for Kittredge, who has been heavily sinker and slider all season.

Naturally, this prompted me to do a little more digging to see if this was an aberration of indicative of a longer trend:

Overall, Kittredge is still only throwing his four-seamer around 10 percent of the time, but has steadily increased its usage over the course of the season. So far in the month of August, he is throwing the pitch 17.6 percent of the time, which is right in line with where it was on Tuesday night.

Kittredge using his four-seam fastball regularly is hardly a new development. The Rays reliever relied on it 18.5% of the time in 2019 when he established himself as a bullpen staple. But he all but ditched the four-seamer in 2020 (albeit in an eight inning sample), and in 2021, it took him until June to throw it more than 10 percent of the time.

With all of that said, let’s talk about why he’s made this adjustment.

Per Baseball Savant, Kittredge’s fastball has 0.1 inches of horizontal movement, which is 7.3 inches below the major league average. This is a little bit misleading, because his four-seamer doesn’t move less than average as much as it moves in the opposite direction relative to the average.

Opposite Direction? What does that mean?

Let’s compare the four-seam fastballs of Kittredge and fellow Rays reliever JP Feyereisen. Their four-seamers are similar in a lot of ways — average spin rate, average velocity, and spin direction. But why does one move so much differently than the other?

That is because of spin efficiency.

I have written about spin efficiency here before, but here is a quick review as it’s relevant to this comparison: spin efficiency is the percentage of spin that contributes to a pitch’s Magnus force based movement. Feyereisen is one of the best in baseball at this, thanks to a four-seamer that ranks in the 94th percentile in spin rate with 92 percent spin efficiency.

Kittredge’s four-seamer, on the other hand, only has 64% spin efficiency, causing it to sink and move slightly to his glove side. Effectively, this means that it is closer to a cutter than it is the traditional four-seam fastball we are used to seeing.

For a better visual, here is a four-seamer from Feyereisen:

And here is a four-seamer from Kittredge from a different game in that series:

Notice how the two pitches start on very similar flight paths, but end up in very different locations. Feyereisen’s stays up, while Kittredge’s takes a pretty sharp left hand turn.

I have already discussed how Kittredge successfully uses his sinker and slider combo to 1) create a pitch tunnel, and 2) coax swings and misses outside the strike zone, but the increased four-seam fastball usage adds a new layer to his repertoire, and a new thing hitters have to consider.

It’s all about location

Since Kittredge’s sinker has great horizontal movement to his arm side, he commands the pitch to the third base side of the plate. Since his slider has great two plane movement both vertically and to he glove side, he frequently commands it to the first base side of the plate. Even though Kittredge doesn’t have a big rising fastball, this doesn’t mean he still can’t use it just as effectively as someone who does.

This big difference between his four-seam usage between now and in 2019 is his command of that pitch. Here is his heat map from that year (catcher’s perspective):

And here is a heat map of four-seamers for 2021:

Notice how the concentrated area is more deliberate this year, up in the zone favoring to glove side, meaning that Kittredge is using its movement to his advantage by creating separation from his sinker and slider.

Which brings me back to Tuesday’s outing.

Of the five four-seamers that Kittredge threw, four of them were on to the glove side of the plate, including a called strike three to Odubel Herrera as well as a big swinging strike three against Brad Miller, just a few pitches after the former Rays infielder made a bid to tie the game.

As a hitter, if you’re thinking sinker or slider and you get that, good luck!

Conclusion

Andrew Kittredge has had a wild career arc, even by the standards of a Rays pitcher. This year, he has established himself as a quality major league reliever, earning his first All-Star selection. For my money, he may be the best option in the Rays bullpen, and that is a high bar to clear.

While the Kittredge sinker slider combo is still his bread and butter, the increased usage of the four-seamer has worked in his favor. Thanks to better command of the pitch, as well as great movement separation, Kittredge is becoming a legitimate three pitch pitcher.

This is especially beneficial to a Rays team that increasingly needs pitchers who can pitch multiple innings. Whether the Rays need a two inning opener, a shut down inning late in games, or a middle inning fireman, Kittredge has proven he can do it all .