Mark Leiter Jr Has Become Shut-Down Lefty Specialist on Strength of Splitter

Mark Leiter Jr. threw 67.2 innings for the Cubs last season over 39 appearances, posting a strong 3.99 ERA and dominating left-handed hitters to the tune of a .176 average and .253 wOBA. That performance was particularly impressive considering it was his first big league action since 2018 with the Blue Jays. You don’t typically see 31-year-old journey hybrid relievers breaking out, but that’s exactly what Leiter did.

The results still felt flukey enough for the Cubs to DFA him and force him to take the long way back by earning a spot again in spring training. He did just that and has emerged once more as a lefty specialist in a bullpen that didn’t have an actual southpaw until Brandon Hughes was activated on Saturday. But with Hughes fresh of the IL and the Dodgers boasting some very strong left-handed bats, Leiter was charged with handling the heart of the LA order in high-leverage situations.

With the Cubs up 1-0 in the bottom of the 6th inning Saturday night, Leiter came in and struck out Freddie Freeman looking before getting both Max Muncy and James Outman swinging. All lefties, all dangerous. Leiter faced just one righty, J.D. Martinez, and hit him with a pitch.

Sunday afternoon saw the Cubs leading 3-2 with men on first and second and one out after Seiya Suzuki dropped a Mookie Betts fly in the sun. Leiter once again sat Freeman down, this time swinging, then gave up a single to Martinez that took a funky hop and ticked off the heel of Dansby Swanson‘s glove to load the bases. Four pitches later, the Cubs saw a 15.5% increase in win probability as Muncy was once again retired on strikes.

“Leit Show’s great,” Patrick Wisdom, who authored some heroics of his own, said after Sunday’s win. “We love when he comes in.”

All the outs he recorded in those two appearances were strikeouts, all against lefties, all on splitters.

That’s the pitch that fueled his breakout last season after seemingly coming out of nowhere, which is fitting because it absolutely disappears on hitters. After getting negative value from the splitter over his first two professional seasons, Leiter worked to perfect it and upped its usage to nearly a quarter of his pitches after being around 17% in the early going. He’s really leaning into the splitter this year, going to over 34% of the time to make it his most frequent offering.

The secret is how effective he’s been at completely killing spin, getting it all the way down to an average of 842 RPMs since the start of last year. That’s the lowest in MLB according to Codify, though Statcast appears to show Aroldis Chapman at seven revolutions lower. Either way, it’s a nasty pitch that has allowed Leiter to carve out an unexpected role as a valuable reliever for a team that looks like it could be very legit.

I just love that the Cubs and David Ross aren’t married to traditional handedness matchups and that the new rules on reliever usage actually play to their favor with a righty who kills lefties. This team was built on run prevention and winning at the margins with small advantages, one of which is Leiter and other members of the bullpen shutting things down about dangerous hitters.

Though it’s still early enough that the numbers can change dramatically over just a couple of outings, it’s hard to dismiss the fact that Leiter has limited 19 lefty batters to a .111 average with a .325 OPS. He’s struck 10 of them out and has walked just one, so even a little regression will still yield a strong line. Having a guy like that who can be counted on to get big outs is a big part of what will make the Cubs much more competitive this season.

You can’t win every game, of course, and there will be more like Saturday where the bullpen isn’t able to hold the slimmest of leads. But what’s more important is that the Cubs are putting themselves in position to win just about every game against every opponent. They get on base, they run well, they play good defense, and the pitching is going to be solid more often than not.

That’s the recipe for success, they just need to keep cooking.

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