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Luke Weaver continues to improve

A developing curveball further enhances the young right-hander’s arsenal

Jeff Curry-USA TODAY Sports

It’s no secret that Luke Weaver has generated his fair share of excitement around here. I am admittedly doing a little cherry-picking with these parameters, but here is every starting pitcher who has logged at least 60 innings since last August, as ranked by xFIP.

Data courtesy of FanGraphs Splits Leaderboards

I don’t think the point requires any more elaboration: Weaver has been nothing short of stellar since joining the Cardinals’ big league rotation in the second half last season. Amidst the pinnacle of his 2017 campaign–a four week stretch in which he posted a 1.49 ERA and 1.59 FIP over six outings–I wrote about the next step Weaver needed to take to assert himself as a frontline MLB starter. I concluded that the key for Weaver would be to develop a reliable third pitch that could supplement his bread and butter fastball and changeup duo.

Weaver increased his curveball usage from 6.89% in 2016 to 11.49% last year, cementing it as his favorite ancillary pitch. Sitting at 20.14% as of this writing, its usage rate has once again nearly doubled this season. However, this usage increase hasn’t been equally distributed across all counts.

Luke Weaver: Change in curveball usage, 2017 to 2018

Situation Δ vs. RHH Δ vs. LHH
Situation Δ vs. RHH Δ vs. LHH
All Counts 7% 10%
First Pitch 15% 30%
Batter Ahead 17% 9%
Even 7% 18%
Pitcher Ahead -5% 1%
Two Strikes 10% 6%

Weaver’s fastball and changeup still comprise roughly 90% of his pitches when ahead in the count or with two strikes. To offset this, he is turning to his curveball disproportionately more often earlier in counts. Weaver has also displayed more confidence in his breaking ball after falling behind to opposing hitters, adding one more pitch for them genuinely consider alongside the fastball and changeup.

As to how Weaver’s curveball has fared in 2018, we don’t have a large enough sample size for me to feel comfortable making sweeping proclamations about the results. That said, the early returns point towards improvement upon last season.

Luke Weaver: Curveball performance, 2017 vs. 2018

Metric 2017 Curveball 2018 Curveball
Metric 2017 Curveball 2018 Curveball
Strike/Ball Ratio 0.67 1.65
SLG 0.385 0.111
xwOBA-wOBA .249-.301 .263-.157
wCB/C -1.26 3.00
Whiff/Swing% 18.6% 13.3%
Foul/Swing% 25.6% 46.7%

While the curveball’s whiff rate is slightly down from 2017, it has been far more effective than ever before according to FanGraphs’ pitch values metric. Sharper curveball control–which QOP Baseball grades in the 96th percentile among all MLB pitchers this season–could be a driving factor behind this success. Compare Weaver’s curveball heatmaps against lefties and righties from a year ago to now.

Heatmaps courtesy of BaseballSavant

The 2018 pitches to right-handed batters are more densely concentrated in the down-and-away corner as opposed to scattering throughout the strike zone. Weaver has evidently done a better job limiting hanging breaking balls up in the zone against all types of hitters.

Embedded in my aforementioned Weaver post is a quote from an excellent piece by pitching guru Eno Sarris at FanGraphs. Weaver told Sarris that he was “talking to Wainwright about what he’s doing in certain counts to make [the curveball] an effective pitch.” Of course, Wainwright’s hallmark curve possesses a “12-6 drop” that his protégé may very well never harness for himself. While Wainwright, standing 6’ 7”, releases his curveball from about 6.5 feet above the rubber to create a steeper downward plane, the 6’ 2” Weaver has a vertical release point that is a full foot shorter than his elder’s. This lower arm slot may hinder Weaver’s ability to conjure up great vertical movement, but he is attempting to compensate for this deficiency with a harder curveball that features more horizontal cut.

I complied a list of all right-handed starters who have tallied at least 30 innings in 2016 (the year of Weaver’s MLB debut) and 10 in 2018 in addition to throwing a curveball at least 5% of the time. I was looking to see who added the most horizontal movement and velocity to their curveball in that timeframe. Sure enough, only one name appeared in the top 10 of both tables.

RHPs with greatest increase in horizontal movement (inches)

Name 2016 CU-X 2018 CU-X ΔHorizontal Movement
Name 2016 CU-X 2018 CU-X ΔHorizontal Movement
Luke Weaver 3.3 6.0 2.7
Jameson Taillon 4.9 7.6 2.7
Adam Wainwright 9.7 12.1 2.4
Michael Wacha 3.8 6.1 2.3
Taijuan Walker 5.6 7.4 1.8
Chase Anderson 3.2 5.0 1.8
Jose Berrios 8.3 10.0 1.7
Kyle Hendricks 8.2 9.8 1.6
Jordan Zimmermann 3.5 5.1 1.6
Mike Leake 7.6 9.0 1.4

RHPs with greatest increase in curveball velocity (mph)

Name 2016 vCU 2018 vCU ΔVelocity
Name 2016 vCU 2018 vCU ΔVelocity
Jesse Chavez 77.9 82.0 4.1
Eddie Butler 80.5 83.8 3.3
Lance McCullers Jr. 85.7 88.1 2.4
Luke Weaver 79.6 81.9 2.3
Jon Gray 78.7 80.9 2.2
Zach Davies 73.2 75.3 2.1
Doug Fister 71.1 73.1 2.0
Luis Perdomo 83.8 85.7 1.9
Vince Velasquez 79.9 81.6 1.7
James Shields 77.7 79.0 1.3

Since arriving at the big leagues in 2016, Weaver has added as much horizontal movement and nearly as much velocity to his curveball as any right-hander in the game. As Sarris detailed, Weaver has proven that he can succeed at the MLB level by adding “more frisbee” to his curveball.

Make no mistake: Weaver is far from flawless. There are reasons to doubt the sustainability of his breakout performance, which still has yet to turn a calendar year old. The 2,164 rotations per minute (rpm) on his curveball are 322 below the league average spin rate, but Weaver has demonstrated pitching proficiency without needing to drop the proverbial hammer using a traditional curveball.

He may not be quite as much fun–or skillful, but that could be a discussion of its own in the comments section–to watch pitch as, say, Carlos Martinez, but Luke Weaver starts have quickly ascended to become some of the game days I anticipate the most.