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Luke Weaver Has Traded Curveballs For Cutters And It’s Working

Weaver’s increased cutter usage is one of the reasons why he’s looking like the great prospect he once was.

Arizona Diamondbacks Photo Day Photo by Christian Petersen/Getty Images

Having been acquired in the offseason as part of the Paul Goldschmidt trade, young right-handed pitcher Luke Weaver is likely to be relatively unknown to most Diamondbacks fans. And seeing as he was acquired for the face of the franchise, he is under incredible pressure from the fan base to perform well. As a former top 100 prospect, he started his career off well, with a 10.9 K/9 and 2.7 BB/9 in his first two Big League seasons (over 96.2 IP). However, Weaver had a down year in 2018, his full year in the MLB, posting a 4.95 ERA against a 4.45 FIP. His strikeouts dipped to 7.99 K/9 and his walks rose to 3.56 BB/9. Certainly, Dbacks fans surely had to be concerned.

So far, through 6 starts, the tune is much different. He currently leads all pitchers on the team with 0.7 fWAR, supported by a 3.73 ERA and 3.35 FIP. His strikeouts are back up to 10.34 K/9 and his walks are currently at a career-low 2.01 BB/9.

It’s still early but there is one big thing that stands out for Weaver in Arizona: he his throwing his cutter more while throwing his curveball and fastball less often:

If you look at 2019, you will see that his cutter has surpassed his curveball in usage. While this change might look a bit subtle, it’s actually important because it’s slowly turning Weaver from a mostly three-pitch pitcher to a four-pitch pitcher. Prior to this year, Weaver was primarily a fastball/changeup type of pitcher. The curveball was supposed to be a good third pitch but it really underwhelmed; prior to this year, his curveball was generating whiffs at a lower rate than his fastball. Furthermore, it was his hardest-hit pitch, with a .321 batting average against and a .211 ISO allowed. Last year, per Fangraphs weighted pitch values, it was the 10th-worst curveball in baseball.

This year paints a different story. His curveball is now the 27th-best curveball in total value in baseball and if you adjust for the rate at which it’s thrown, it’s the 22nd-best curveball out of 97 pitchers.

Thanks to the rise of the cutter, Weaver is able to pick his spots better on how he uses the curveball:

Luke Weaver Curveball Usage

Situation 2018 2019
Situation 2018 2019
First Pitch (LHH) 25% 32%
First Pitch (RHH) 19% 15%
Batter Ahead (LHH) 10% 2%
Batter Ahead (RHH) 12% 7%
Even (LHH) 19% 17%
Even (RHH) 14% 8%
Pitcher Ahead (LHH) 7% 6%
Pitcher Ahead (RHH) 8% 5%
Two Strikes (LHH) 9% 3%
Two Strikes (RHH) 8% 4%

This is a pretty large table but what stands out is how Weaver is now using the curveball: he is primarily using it to steal strikes against left-handed batters. He has dropped its usage against right-handed hitters considerably. But the biggest takeaway is that he rarely uses it as a “put away” pitch anymore (e.g. when the pitcher is ahead in the count and/or has two strikes).

The early results have been tremendous. Weaver has upped the whiff/swing% of his curveball from 18.45% in 2018 to a massive 54.55% in 2019 - the third-highest rate in baseball (minimum 40 curveballs thrown). Furthermore, batters aren’t putting it in play: only 2 out of his 47 curveballs have been put into play this season (4.3%). Last year, batters put a massive 20.7% of his curveballs into play.

There are two factors at play here. The first is how he’s using it as seen above. The other factor is where Weaver is throwing the pitch:

This is a pretty interesting twist. Generally, when a pitcher is throwing a pitch to “steal strikes” when the count is even, usually it’s in the zone for a called strike (see Patrick Corbin’s “curveball”). Weaver has opted to just stop throwing it in the strike zone altogether. And considering that batters can’t seem to hit it, it makes sense.

Which leads us to Weaver’s cutter. The focus on this article when Nate Rowan found something really interesting about Weaver’s cutter in his excellent start against the Pittsburgh Pirates last week:

Just look at that location. Absolutely pounding the edge. That’s a pitch that both right-and-left-handed hitters are going to struggle with if he can hit that spot consistently (see: Mariano Rivera’s entire career). Remember how Weaver mostly stopped throwing his curveball to righties? He replaced that curveball usage by primarily throwing his cutter to right-handed hitters.

Weaver is pretty much using his cutter just like Mariano Rivera did. He uses it to pound the edges of the zone to either get whiffs or really poor batted ball contact. He’s getting a solid 22.58% whiff/swing%, which is a strong number. The real beauty, however, is the batted ball profile of his cutter:

  • Groundball%: 54% (12th-best in MLB)
  • Popup%: 23% (2nd-best)
  • Flyball% 8% (2nd-best/2nd-lowest)

Put all of this together and Weaver is sitting on the 11th-best cutter on a rate basis per Fangraph’s pitch values.

Essentially, we’ve simultaneously seen Luke Weaver add a fourth pitch to his arsenal as well as make a pretty substantial adjustment in how he throws his curveball all in this past offseason. The end result is a pitcher that looks to be really, really promising.

Weaver may not have the strikeout potential of Robbie Ray, but he’s clearly got the stuff to be a very good strikeout pitcher. Where he really excels compared to Ray is that he has excellent command. Weaver’s 5.2% BB% is the 15th-lowest walk rate among MLB starters (95 total qualified starters) and this is something that has been pretty consistent in his career. He’s already known for his very excellent changeup.

The early returns on Luke Weaver are extremely promising. The Diamondbacks have him for FOUR more years after this season. He’s already got the stuff and the makeup to be a #2 pitcher and he seems to be the perfect mold for a potential future ace. Even if he doesn’t reach that ace potential, if Luke Weaver continues to pitch like this for four more years, he alone is going to make the Paul Goldschmidt trade appear extremely lopsided in favor of the Diamondbacks.