At least for now, the Cubs are battling a big-time Mark Leiter Jr. problem

When that splitter is working, Mark Leiter Jr. has shown he's more than capable of neutralizing both left and right-handed hitters on any given night. The matchups seemingly don't matter to the 33-year-old, a good sign for a Chicago Cubs team that hasn't had a shutdown lefty reliever in some time.

But similar to what we saw down the stretch last summer, when Leiter Jr. became completely ineffective down the stretch, posting an 8.59 ERA and 2.318 WHIP in 10 September appearances. He completely lost the ability to throw that splitter and, without it, he got torched.

Things have gone sideways for Leiter Jr. again of late, but it doesn't seem to be an issue with his splitter, as the numbers are still overwhelmingly positive there. But after slamming the door regularly in April (0.69 ERA in 14 appearances), he's been a shell of that with an 8.00 ERA in May and a 10.80 ERA here in June.

It's been a rocky stretch for Cubs reliever Mark Leiter Jr. - similar to what we saw last September, when he faded hard down the stretch

Dating back to May 25, Leiter Jr. has made 11 appearances, allowing an .805 opponent OPS, due at least in part, perhaps, by a bloated and unsustainable .475 BABIP. His 3.40 FIP suggests a good deal of bad luck during this stretch, well outpacing a 13.50 ERA during this stretch.

His primary pitch this season, a sinker, has been hit hard - to the tune of a .293 BA/.312 XBA, way up from last year, when he recorded a .134 BA/.234 XBA on the pitch. That's proven costly. His splitter has been even better than it was in 2023, with opponents hitting just .067 BA against the pitch with an equally chilly .098 XBA.

There's been a change in his pitch mix this season, as he's largely gone away from his cutter in lieu of more sweepers - a pitch he hasn't thrown prior to 2024, according to Baseball Savant. He hasn't found much success with it yet, giving up a lot of extra base-hits in the process.

The hope has to be that he can get one of those pitches - his sinker and/or sweeper - dialed in. He can't just throw splitter after splitter. There has to be setup pitches in the attack plan and, unfortunately, the numbers suggest he just hasn't had a good feel for them and hitters are making him pay for it.