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Surprise, surprise. Shota Imanaga was excellent AGAIN last night, striking out 11 Oakland A’s at Wrigley Field en route to his 18th quality start of the season.
Imanaga’s final line — 6.0 IP, 5H, 2ER, 3BB, 11K — beautiful as always. Oh, and get this: by game score (59), that was only his 13th-best start of the season. That’s how good he’s been in 2024.
Indeed, he’s been pretty close to automatic this season. Yes, there were the three “blow-up” outings against the Brewers, Mets, and Guardians, but in each of his 25 other starts, the Cubs had — at the very least — a shot to win.
So after last night, Shota Imanaga’s full-season numbers look pretty darn good: 3.03 ERA, 25.4 K%, 4.2 BB%, 28 starts, 166.1 IP. And if he gets two more starts to end the year, he’ll have a good shot at ~180.0 IP and a sub-3.00 ERA. That’s pretty much the extreme-best version anyone could have realistically hoped for when the Cubs signed him last offseason.
He’s already exceeded his “mid-rotation” upside projection and has entered into the realm of “possible front-of-rotation” starter. How good could he be next year?
That’s kind of the context I wanted to keep in mind while discussing the one wart we’ve always known was going to be there: the homers.
Shota Imanga and the HRs
After allowing another home run last night, Shota Imanaga has now allowed 15 HRs in the second half of the season (2nd most in MLB) and 27 HRs all year (t-6th most). Most of the pitchers around him on those lists have ERAs roughly 1.5 runs (or more) higher. So what’s the difference? Well, Shota Imanaga manages to succeed despiteꦅ the homers because most of his come w🔯ith no (or few) men on base.
And while that’s OBVIOUSLY not all luck — he’s a very good pitcher and his strikeout/walk marks are within his control — he is benefiting from an unusually low .213 BABIP in the second-half of the year, during a stretch when most of his homers came bunched up (1.95 HR/9, 2nd highest in MLB).
That’s really more to the point here, as the potential problem seems to be increasing right alongside his ERA:
Mid-analysis reminder: Shota Imanaga is still a very good pitcher even with this issue. Criticism is not the point. Instead, the point of this call-out is to address what is potentially limiting him from becoming/maintaining a position as a TOP of the rotation arm.
Why or how is this happening? Well, if I had one guess (based on the following graph), I’d say opposing batters have decided on a different approach against Imanaga — one that sells out for homers, knowing they otherwise have very little chance at success.
the increase in pull rate and hard co💝ntact as the yeܫar has gone on:
We could probably take this a step further, noting that most of the slugging damage is coming on his four-seamer, which has been steadily losing velocity as the season has gone on. I think Imanaga’s aware of that fact, too, because the volume of four-seamers he’s been throwing has decreased right alongside the velocity:
Imanaga has a variety of effective pitches, but it was and is his uniquely-shaped four-seam fastball that has driven so much of his success in Japan and in MLB. And although premium velocity wasn’t the key there, it’s not like it doesn’t matter at all.
I suppose that’s all an associated concern for a 31-year-old pitcher: If Shota Imanaga’s top-of-the-rotation status is based on his ability to continue limiting homers … and his ability to continue limiting homers is based in part on the effectiveness of his unique fastball … and if his fastball is losing velocity as he approaches a career-high in innings pitched, well then that’s something to watch next year.
But wait, there’s one more chief concern: His home ballpark.
The Wrigley Field Factor
As you may have heard by now, Wrigley Field has played extremely pitcher-friendly this year, especially when it comes to home runs (a park factor of 86 this year, while league average is scaled to 100). Only four parks played more pitcher-friendly when it comes to h🐲omers.
Normally, that’d be a good thing, because you might think “Hey, his home park matches his skillset!” But that’s not how Wrigley Field works. Thanks to the wind, the degree of homer-friendliness at this park changes more dramatically than almost any park in baseball. For example, last season, Wrigley had a HR park factor of 105 (11th highest). And in 2021 it was 124 (fourth most homer-friendly!).
So let’s just say, if the wind had blown this year the way it had in 2021, Shota Imanaga would have given up a LOT more homers than he has, and he has given up a lot as is.
You can’t QUITE do this — and I’m fudging the math just to illustrate the point — but if Wrigley’s HR park factor next year was, say, 115, Imanaga might expect to see roughly a 30% spike in homers allowed at home, with no change at all in his own peformance. That would mean roughly four more homers allowed, and roughly six more earned runs, increasing his ERA from 3.03 to 3.35. See what I mean? That one ballpark change takes him from near-top-of-the-rotation to more “really good mid-rotation starter.”
So that’s basically the concern for next season. Or at least the two things to keep an eye on: Imanaga’s fastball velocity/effectiveness, and the Wrigley Field home run factor. He’ll be a valuable member of the rotation either way, but just HOW valuable can vary well, like the winds at Wrigley Field.
Brett Taylor contributed to this post.
