Ronald Acuña Jr. is seeing a lot more four-seam fastballs this season. Last year 30.9 percent of the pitches thrown to the Braves slugger were four-seamers. This year... 39.4 percent. "Why would that be a problem for him," Eno Sarris rhetorically asked on From The Diamond with Grant McAuley. Sarris then explained why.
"He's a guy with plus bat speed that used to launch these four-seamers," Sarris said of Acuña. "He does really well on high four-seamers, but what the league kind of figured out is that he'll hit the low four-seamer into the ground, or maybe even swing through it. He's being pitched differently."
Sarris explained to McAuley that he feels Acuña is physically healthy, similar to last season, particularly in sprint speed and bat speed. The reason why Acuña's slash stats and power numbers are down might be because the league has adjusted to him.
"What happens when you throw low four-seamers, my theory is Acuña sees low and has a swing he can put on a slider, and when he sees high he has a swing he can put on a fastball. What the league has said is 'Ah, what about low fastballs?'
"If you look at the heat maps he's getting more low four-seamers than he's ever gotten. Usually pitchers don't throw the low four-seam because the four-seam is all about jumping up on the hitter, ride, swinging underneath it. But in this case the league has said 'OK, he might make contact with this, but it won't be a homer and I'll take that ground ball from you.'"
The next step for Acuña will be to make an adjustment of his own, which might not be as easy as it sounds, Sarris explained.
"Now you're seeing a lot of sliders and four-seams low and you have to figure out what you're going to do," Sarris told McAuley. "Are you going to do more of a four-seam swing down there and lift those four-seams and then moss more sliders? That might be why his strikeout rate is up a little bit. He's working through his way of 'What's my response to this newest book on me?'"
Sarris told the story of Mike Trout, who was susceptible to high pitches. He spent an entire offseason working on a swing to hit balls up in the zone. Pitchers still throw Trout high, but he can now hit those pitches out of the ballpark.
"The best players find ways to battle," said Sarris.