Jon Lester pitches tonight against the Cardinals in St. Louis, and how he performs in that start may have some impact on his postseason rotation spot. The 33-year-old lefty is in the middle of his worst season by most metrics, and he’s had an ERA over 5.00 in the second half, so it’s only gotten worse. There are plenty of reasons to be worried about the pitches the Cubs starter is throwing right now. Even more worrisome might be the pitches he’s not throwing anymore, though.

Time comes for all of us, so it’s not surprising that Lester’s stuff has declined. It’s just that it’s happened across the board, to all of his pitches, in almost equal amounts, that makes it noteworthy. Consider that he’s currently showing:

The worst fastball velocity of his career.

The worst four-seam fastball spin of his career.

The worst four-seam ride of his career.

The second-worst curveball velocity of his career.

The worst curveball drop of his career.

The worst curveball cut of his career.

The worst cutter velocity of his career.

The second-worst cutter drop (relative to fastball) of his career.

These things are all meaningful to the outcomes of the corresponding pitch types, and in many cases, the career-worsts are not just incremental. For example, his fastball velocity is the worst of his career by a full tick, and his curveball has lost nearly a full inch of drop since just last year, only the second time in his career that he’s had a movement change as drastic.

Sometimes, a pitcher’s release point drops as he ages, and he trades vertical movement for horizontal movement in the process. That’s generally happened for Lester, at least in terms of the dropping release point:

But you might notice right away that he’s been throwing from the same slot for the last three years, so that doesn’t really explain this year’s difficulties. Notably, the lower arm slot hasn’t really helped either his horizontal movement, which has been steady, or his ground-ball rate, which is related to horizontal movement and has been in lock step with his career rate for some time now.

With all of this erosion of stuff in front of us, it’s sort of surprising, then, that his strikeout rate is still so close to his own average, and still so impressive, at 23.5%. Even though he’s one of the that group who have gotten worse relative to the league by remaining the same, Lester’s strikeout rate is still a couple points better than league average and three points better than the average starter’s.

No, it’s batted balls that have created the most trouble for the left-hander. At .313, he’s recorded the worst batting average on balls in play of his career, but a couple other seasons have been as bad or nearly as bad. What’s really remarkable is the home-run rate, which is nearly 55% worse than his career average.

We could wave some of that away with the current home-run environment, but the league is only up about half of that. So perhaps we could add the league effect to the declining stuff and offer that as an explanation for most of Lester’s troubles. But there’s also a pitch that Lester isn’t throwing any more that may help explain much of this situation, as well.

Take a look at his four-seam location to righties in 2016 (from the catcher’s view):

And now in the second half of 2017:

Lester isn’t throwing his four-seamer up and in to righties like he used to, and/or he’s missing middle-middle with it by accident. We know, thanks to Travis Sawchik’s excellent Big Data Baseball, that the Pirates once famously found that the pitch on the outside part of the plate is more effective if preceded by a pitch on the inside part of the plate. So, given the fact that Lester is throwing fewer pitches inside to righties, it shouldn’t be surprising that the lefty has been giving up homers to righties at a rate that’s 72% worse than his career average.

Lester’s four-seamer is doing worse than it ever has by pitch-type values, and we covered its spin and velocity and movement issues. Maybe he can’t throw it past righties on the inside, is the problem. Maybe he can’t place it up and in like he could before. Maybe he just doesn’t think he can.

For whatever reason, though, it’s the absence of that pitch — as much as the presence of the diminished stuff on the other pitches — that’s become Lester’s biggest current problem.