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How Could Luke Weaver Reduce His Fly Ball Rate?

Luke Weaver on the mound.
Luke Weaver on the mound.
Photo by Ralph Freso/Getty Images

As it happened, Jack Sommers’ comment ignited my curiosity.

“...the BIGGEST key for Weaver in 2021 is to reduce his FB rate, which skyrocketed in 2020. ...Perhaps an improved cutter, or maybe just better command...” — Jack Sommers.

Jack Sommers

My questions were, “How could Luke Weaver reduce his fly ball rate,” and “How much improvement could he expect?” Let’s look at those questions.

How could Luke Weaver reduce his fly ball rate?

Reduce Spin Rate. One way to reduce his fly ball rate could be to reduce the spin rate on his 4-seam fastball (Source). The tradeoff would likely be reduced strikeouts.

A reduced strikeout rate would be worrisome because a study referenced in this article found, “Pitchers with higher strikeout rates had better ERAs and WHIPs than pitchers with lower strikeout rates, regardless of ground ball profile[rate].” Likely that finding applies regardless of fly ball rate, too. Reducing his spin rate is not a good option.

Change Arsenal of Pitches. Another way would be to change his arsenal of pitches. A study grouped pitchers into 6 clusters by their arsenals. The following table shows the fly ball percentages with other statistics:

Clusters of Pitchers.
Clusters of Pitchers.
Charlie Marcou. 2017-2019 seasons.

The table shows the Sinkerballers’ 19.1% fly ball rate was the lowest. That group had the lowest barrel rate (great!), the second highest wOBA (ouch) and the lowest K% (ouch).

Two alternative groups (Cutterballers and Sinker-Sliders) had lower-than-average fly ball rates with better wOBA and better K%. Accepting an extra 3% fly balls in return for better results (.010-.015 lower wOBA and 4-5% higher K%) looks like a winning tradeoff.

11.8% of Luke Weaver pitches are cutters, so it looks like he is in the Cutterballers, the best cluster to be in. He is in good company because the study listed teammate Madison Bumgarner in the same cluster. So, changing his pitch arsenal is not an option.

Better command (see Jack Sommers’ comment). Better command is always an advantage to the pitcher because he can confidently pitch in the shadow zones (those attack zones between the heart of the plate and the chase zones).

wOBA in Attack Zones.
wOBA in Attack Zones.
Baseball Savant. 2020 season.

The table shows while increased command (with more pitches in the shadow zone) would help most of the Diamondback starters, the benefits of increased pitch command are less clear for Luke Weaver, Alex Young and Zac Gallen:

  • Pitching in the shadow zone was a clear advantage (compared to the zones adjacent to it) for for Madison Bumgarner, Taylor Clarke, Merrill Kelly, and Caleb Smith.
  • Pitching in the chase zone was a clear advantage for Zac Gallen.
  • The chase zone or shadow zone were about the same (with both preferred to the heart of the plate) for Alex Young and Luke Weaver.

Improve his cutter (see Jack Sommers’ comment). His cutter is unique (Jack called it a cutter/slider combo). Perhaps that uniqueness is an opportunity for improvement. How good is Luke Weaver’s cutter? The following table compared Luke Weaver’s cutter to other starting pitchers for the Diamondbacks.

Cutters by Diamondback Starting Pitchers
Cutters by Diamondback Starting Pitchers
Baseball Savant. 2020 Season.

On the plus side, Luke Weaver’s cutter had the second highest whiff rate. On the minus side, Luke Weaver’s cutter had the highest wOBA. Improving his cutter looks possible.

How much improvement could he expect?

Improvement of Luke Weaver’s cutter looks like the best option. A reasonable improvement is to achieve an wOBA of .3615 (average of the cutters of the other four Diamondback starters). This improvement would have lowered Luke Weaver’s wOBA by about 2% (from .362 to .356 in 2020).

Without the improved cutter, FanGraphs’ projection (steamer) for Luke Weaver’s 2021 ERA is a 29% improvement. However, wOBA is more like FIP because how FIP is designed. FIP was projected to stay about the same. That FIP projection means his projected wOBA would change less than ERA, although I don’t know by how much. Improving his cutter would lower his projected wOBA.

Luke Weaver’s Fly Ball Rate

In 2020, his 48.4% fly balls was a career high and significantly above his career average of 36.3% (FanGraphs). Countering that negative development was that in 2020 his 19.3% line-drives was a career low and significantly below his career average of 23.2% (FanGraphs).

Any improvement is worth the effort! A good question is, “Would improvement of his cutter impact Luke Weaver’s fly ball rate?”

It’s unclear how much his fly ball rate and line-drive rate will change next season. In any case, it will be worth watching.