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Diamondback Fastball Trends

With better than average fastballs, in September cutter fastballs spiked.

Madison Bumgarner.  Cutters break towards the glove side.
Madison Bumgarner. Cutters break towards the glove side.
Photo by Lachlan Cunningham/Getty Images

In the last two season, the Diamondbacks increased the frequency of fastballs. While their velocity was below the average in the Majors, in the last two seasons the spin rates were above average, albeit that the difference was small in 2021. For details see the following table.

Data from Baseball Savant.

For the Diamondbacks, the proportion of fastballs that were cutters spiked in 2020 and in September 2021. For details see the following table.

Data from Baseball Savant.

What are cutters and why can they improve pitching results?

Some writers say cutters are a hybrid pitch with characteristics of a fastball (velocity is only a few mph slower) and sliders (break is similar but less). My view is that some pitchers’ cutters have a stealth break that is just enough to prevent hard contact, and for other pitchers their cutters’ late break totally surprises hitters. An example of the latter was Hall of Fame pitcher Mariano Rivero. I saw a video of his cutter. It looked like a pitch well off the plate and broke over the plate for a called strike.

Cutters can improve pitching results either by reducing hard contact or by whiffs and called strikes.

Dan Haren, Diamondbacks Pitching Strategist, pitched outstanding cutters. He was voted the 9th all-time best Diamondback per this AZ Snake Pit article. Did he discover effective ways to incorporate them in pitching strategy? Is the effectiveness of cutters enhanced in combination with pitch location and other types of pitches? Did he discover that cutters effectively counter the latest batting trends? Although these are questions instead of answers, they could help explain the spike in cutters.

This season, which pitchers had the most cutters?

The following table shows that in 2021 Madison Bumgarner’s 786 cutters were more than the total cutters of Merrill Kelly (333), Tyler Gilbert (271), and Zac Gallen (175). From another perspective, Tyler Gilbert pitched the most cutters per inning; Madison Bumgarner pitched the second most per inning. Data was from Baseball Savant’s pitch arsenal leaderboard.

Merrill Kelly’s cutters had the lowest rate of hard hits (22%) and put-aways-on-2-strike-pitches (25.3%). Madison Bumgarner’s cutters had the highest rate of whiffs (21%).

2021 Season. Data from Baseball Savant’s pitch arsenal leaderboard. Caveat: Brooks Baseball has significantly different counts on cutters pitched.


In 2021, three of the four Diamondback pitchers who pitched the most cutters were the three pitchers with the most innings for the Diamondbacks. The cutter was an effective pitch for Madison Bumgarner (whiff %) and Merrill Kelly (hard hit % and put away %).

Cutters had more whiffs and less hard hits than other fastballs. In September, they had less homers per pitch. Possibly, cutters are an effective tool in implementing pitching strategy. For the Diamondbacks, it’s likely that cutters will be an important part of next season.