MLB Playoff Rotations, and Zack Grienke’s first month in Houston

With the calendar’s turn from August to September, we officially passed the one-month mark since the Trade Deadline, which of course means that we now have a month’s worth of games featuring the Astros’ new number three starter, Zack Greinke. So how have things worked out for Houston thus far since assembling their triple-ace rotation?

Well, Justin Verlander and Gerrit Cole have looked just as dominant, and Wade Miley looks about as competent as he did before the deal. And Greinke has looked…fine. Not bad or anything, but definitely not up to the level he was at an Arizona, with an ERA that’s risen nearly a full run and a WHIP that’s up nearly 0.40. He’s still a fine starter, of course; in this year of the juiced baseballs, a 3.86 ERA is still good enough to be significantly above-average.

But this is a guy who was definitely a part of the Cy Young discussion in the NL pre-trade, so it does feel like a bit of a step back. So let’s try and break this down: how exactly has Zack Greinke changed in Houston? And is there anything he can do to change it back?

My first instinct is to look at factors that are more in the realm of luck. After all, panicking over stats for the season in late April and early May looks silly; often, there are still players on lucky or unlucky streaks that wouldn’t be at all sustainable over much longer than a month. Just because we’ve moved our one month cutoff from “start of a season” to “stats for changing leagues” doesn’t change that underlying principle.

And sure enough, at least some of what’s driving Zack’s ERA increase is a change in things that are less in his control: his strand rate is down somewhat (77.5% with Arizona to 69.8% since the trade), and his batting average on balls in play is up quite a bit (.263 to .310). Of course, that doesn’t explain all of the change in his numbers.

His FIP, which ignores stats influenced by those things, is still over a run higher since the end of July as well (from 3.20 to 4.24), so there are some other things going on. And even within his batted ball rates, there’s some weirdness. For instance, both his hard and soft hit rates are up (with the 8 point drop in medium hit rate split between those two), and his ground ball rate has gone up 7.5 points, at the expense of both his line drive and fly ball rates. Those are all slight changes, but none of them seems especially worrisome or anything.

As for the factors that contribute to FIP, Greinke’s HR/FB rate is up slightly since the trade, but less than three percentage points overall (10.8% for the Diamondbacks, 13.5% for the Astros). His walk rate is also up a percent and a half, but the biggest change is to his strikeout rate, where he’s seen a drop of nearly 7%, from 24.0% to 17.2. Of course, some sort of drop is to be expected once you account for the change in leagues, since NL pitchers get a chance to rack up strikeouts on pitchers, but that still doesn’t account for everything here: Greinke’s K% against non-pitchers this year is still 20.5%, and he’s even already gotten an interleague game under his belt in his first six AL starts since 2012, so there is something else going on.

Thankfully, it doesn’t seem to be a case of losing his stuff. Going by Fangraphs’ pitch velocity numbers, his fastball, curve, and changeup are all within half a mile per hour of his velocity with the D-backs, and his slider has actually been up nearly two miles per hour on average since the deal, so it doesn’t seem like it’s an injury. And his pitch selection seems mostly the same; assuming Zack throws a 100-pitch game, he’s essentially just throwing 4 more changeups and two fewer fastballs and curves per game. That’s not exactly a huge shift.

As far as plate discipline, there are no major changes at the top-line level. Batters are still swinging at and making contact with a similar number of pitches. The biggest changes are at the more granular level: batters facing him are swinging at about 5% fewer pitches in the zone, and while their contact on pitches outside of the zone has dropped nearly 5% (from ~70% to 65), there’s been an even bigger gain in contact on pitches inside the zone (from ~85% to 91.5).

Basically, it seems that batters are doing a better job at waiting for Zack to make a mistake in the zone and punishing him, and we’re still early enough into his Houston tenure that a few extra mistakes still shows up in his stat line in a notable way. It’s something to iron out over time, but given that none of the other underlying factors are sounding the “something’s different and wrong” alarm, it seems to be the type of problem that the Astros can mostly just wait to sort itself out.

Of course, even if it doesn’t and this is just how Greinke throws the rest of the year, the Astros are still pretty well-positioned for October. MLB.com posted their predictions for playoff rosters, and the Astros’s starting four-man still stacks up with the best of them:

The Rays and Indians are strong competitors, but both of their averages are buoyed by unsustainable small sample sizes of their own (the injured Tyler Glasnow and the recently called-up Aaron Civale, respectively, are carrying sub-3.00 FIPs and >200 ERA+s in under 10 starts). Those two and the Nationals are also all fighting for the Wild Card, and depending on how the A’s finish and the Wild Card games go, there’s a chance none of those three even make it past the one-game play-in. The only other team with a rotation this strong that is a sure thing to make the DS round is the Dodgers, and that’s pretty good company to be in.

Either way, one month into the Zack Greinke trade, and even if Zack has looked a little rougher than pre-trade, the Astros overall still look better with him on the team than without him. Of course, any concerns about his performance may also be short-lived, and things could still even get better for Houston’s rotation before the season ends.