Platoon splits have become a major part of baseball today. The Athletics have ridden a split of Jaso and Norris to production from their catcher position. Many left-handed starters have had success against righties and many have struggled. Over the course of his career Cole Hamels has had more success against RHB than LHB (.294 vs .301 wOBA). Hamels is known for his best pitch — his change up — which has helped him neutralize RHB throughout his career.
So often when a LHP struggles against RHBs the common fix is to use a change up more often or to improve the change up. However, for some pitchers this model does not work. Dallas Keuchel, a pitcher who used a change up as his primary offspeed pitch against RHBs in the beginning of his career struggled still against righties. As shown in this article, from the time his career began until May 31st of this season Keuchel was one of the worst starting pitchers against RHB. However, by breaking this down season by season it can be seen that Keuchel’s numbers have actually improved as his career’s progressed.
The key to Keuchel’s increased success against opposite-handed hitters seems to be found in his pitch selection.
Keuchel has been an often-discussed topic on this site this season. The key to his success this season has been his increased use of his rapidly-improving slider which was covered by Eno Sarris here. As Sarris states the slider will allow Keuchel to have increased success against lefties. However, looking at Keuchel’s splits this season shows he has improved his numbers against righties significantly. According to PitchF/x data Keuchel has used the slider significantly more against righties this season. He has done this at the expense of four-seam fastballs opting to throw more two-seamers and sliders.
While he is still using the changeup at around his career averages, his heavy increase of sliders in the biggest difference in his way of attacking hitters. As his numbers for the season have shown he is limiting home runs and striking out the highest percentage of right-handed hitters in his career. This has also lead to a significant improvement in his wOBA allowed. This season against righties the slider has produced a better than MLB average whiff rate (18% vs 13.%).
Keuchel provides an blueprint for other left-handed starters who struggle against righties. Contrary to typical belief that in order to improve against opposite-handed batters pitchers must develop their change up, Keuchel has begun using his best offspeed pitch — the slider — more as a putaway pitch against off-handed batters. Keuchel has become the poster boy for pitching to strengths, riding his sinking two-seam and slider to a breakout season while significantly improving his platoon splits.
Another pitcher who was mentioned as the worst in the league against righties was Eric Stults. Stults, a lefty like Keuchel, features both a slider and a change up. Additionally, much like Keuchel, Stults’s best offspeed pitch according to pitch values is his slider. However, looking at his pitch selection to RHB he has used the change more than twice as much as the slider since 2007 (25.6% vs 10.8%). If Stults followed in the footsteps of Keuchel and began to use his best pitch more against opposite-handed hitters it could cause him to minimize his platoon split and make him a better all-around starting pitcher.
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