Over his four year career, Adam Kolarek has grown a reputation for being one of the best lefty-killers in the MLB. With a low arm slot and bowling ball sinker, he is a tool perfectly designed for today’s specialization and bullpen heavy game. 

Against left handed batters, the scouting report is pretty straightforward: A heavy dose of sinkers with an occasional slider. Like so many one pitch wonders of the past, hitters just can’t figure it out. Or more specifically, left handed hitters can’t figure it out.

He can basically throw the same pitch every time against lefties, but has struggled being passable against righties throughout his career. Much of this platoon imbalance is due to his sinker’s decreased effectiveness. It goes from a devastating bat-misser to a subpar barrel-finder.

The OPS difference in Kolarek’s platoon split – how he matches up against batters of different handedness – is comparable to the OPS difference of Jeff Mathis and Josh Donaldson over the past four years. Needless to say he’s had reason to experiment with ways to scrape by against righties.

To compensate for the sinker’s decreased effectiveness, changeups and four seam fastballs are thrown into the mix. As interesting as his sinker’s platoon dynamics may be, it is actually his four seam that interests me the most. 

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— Johnny Asel (@JohnnyAsel) November 7, 2020

The goal in arsenal composition is usually to have each pitch coming out of the same armslot and stem off of one another. This is the case with his slider, changeup, and sinker, but not the fastball. While the other three come out of the same window, the fastball release is on an island. The overlay above shows he tips the fastball mid motion with his glove, so why does he do it?

To answer this question, we must examine the fourseam-sinker dynamic. Four seamers generally sacrifice quality of contact for missing bats. Meanwhile sinkers get weaker contact and fewer whiffs. Four seamers try to get above the barrel, sinkers try to get below the barrel. 

The best sinkers – like that of Kolarek – succeed because they get below barrels even when the hitter knows it is coming. However, what usually makes the best sinkerballers great – having inefficient or horizontally shifted axes – also tends to make them have below average four seamers. With Kolarek’s sinker diving as much as it does, he would need a large relative movement difference to make his four seamer work out of the same arm slot. So rather than trying to achieve an insane relative movement gap, he has instead pursued a large absolute movement gap out of different arm slots, and it works.

The higher armslot adds two miles per hour and a bunch of backspin optimizing the pitch to get whiffs. Righties are so locked in on his diving sinker-changeup combination, each four seamer is basically a surprise attack. He reduced its usage this year, but in past years he would occasionally spin a curveball or slider out of the high arm slot to keep batters even more uncomfortable.

As he has become increasingly formidable against right handed batters, he has shifted away from the four-seamer. Just because he is moving away from it does not mean it was a bad pitch; fangraphs has it as an above average pitch each of the last two years. Rather the pitch was like training wheels. It steadied him when he was not ready, but is no longer a necessity. If he has finally found a way to make his sinkers work against righties, there is no sense in giving them a chance with the four seamer.

Kolarek’s sinker makes him an outlier, but that also means he has to add pitches to his arsenal unconventionally. The uniqueness of his sinker made adding a four seam difficult, so he went about it a different way. Like Patrick Corbin’s curveball, sometimes the pitcher’s best weapon is surprise. It is not something recommended to all, but perhaps a concept that could aid the arsenals of the super sinkerballers in the league.