First things first: I've been writing about the Angels a lot lately. I don't know why that is, and it isn't going to continue. But bear with me just one more time. I promise it might or might not be worth it.
Now then, the other day we published an analytical piece about Jered Weaver, which you can read here. It was inspired by the following quote from an anonymous Seattle Mariner, talking about which Angels starter is the most difficult to face:
"Except," added another player, "when it's daylight in Anaheim, and Weaver is throwing out of the rockpile background."
Angel Stadium has a rockpile background just left of dead center. The Mariners player said that during the day time, it can be hard to read the ball out of Weaver's hand because with his delivery and lanky frame it looks like he's pitching out of the rocks. He'd be pitching out of the rocks at night, too, but it stands to reason that during the day, the rocks might be brighter and more distracting.
Anyway, you can just read that original article if you missed it. Here's what we found when we separated Weaver's home starts during the day from Weaver's home starts at night:
I removed innings pitched from the original table because it's superfluous, and I removed ERA from the original table because it's stupid and frequently misleading. What this table shows is that, at home during the day, Weaver has missed a lot more bats, and allowed far fewer home runs. That suggests that, indeed, batters can have a hard time seeing the ball.
We already covered all that ground. I wanted to try to take it a little deeper. The remainder of this post is going to have a lot of data tables. This post required hours of research that might not have been worth the time, but the time's already gone and the work's already done, so the only thing left to do is to share the results.
The first thing I wanted to check was Weaver's day/night splits on the road. Maybe it isn't about the rockpile. Maybe Weaver's just a better pitcher during the day for some reason. Here's what I found:
During the day on the road, Weaver has missed a few more bats, but not to the same degree. Look at that home-run column, though. We see a difference almost as big as the difference in the first table. That casts doubt on the difference in the first table being meaningful. It doesn't prove that the difference in the first table isn't meaningful, but it's a consideration.
After I was done comparing Weaver to himself, I set about comparing him to other long-time right-handed Angels starters. Those starters are Ervin Santana, John Lackey, Kelvim Escobar, and Bartolo Colon. All four of those guys started a lot of games in the same ballpark in front of the same rockpile, and because they're right-handed, they had a shot at hiding the ball in the rocks, too.
I know that's a lot to digest. It's also hard to know what to make of this. Three of the four guys don't show any home-run reduction in the day time, but Escobar does. All four guys show improved ability to miss bats to varying degrees, but not like Weaver. We see that Colon's contact rate drops from 87 percent to 82 percent, which is pretty big. Weaver drops from 79 percent to 71 percent. Because we're dealing with contact rate, by the way, the sample sizes aren't so small. Instead of plate appearances, the denominator is swings.
Finally, I took a look at a couple long-time left-handed Angels starters: Jarrod Washburn and Joe Saunders. It seems to me that lefties shouldn't benefit in any way from the rockpile. It's just not where the hitters are looking. The data:
Interesting about the home runs. Anyway, both Washburn and Saunders show slight improvements in contact rate during the day. Every pitcher we've looked at has shown at least a slight improvement in contact rate during the day. It might be that it's just generally a little harder to hit the ball during the day. It might be that the average day game features a slightly worse lineup than the average night game, since day games frequently follow night games and regulars can get those day games off. It might be something else, or a combination of things, or nothing at all.
Where has this all taken us? Nowhere conclusive, still. We can't declare anything about Jered Weaver and the outfield rockpile. Since the first article, I'm less sure that there's anything meaningful about Weaver's home-run reduction during the day. I'm more sure that there's something meaningful about his increased rate of missed bats, but the benefit might be of a smaller magnitude. Washburn and Saunders missed more bats during the day, too, and they weren't hiding their pitches in the rocks.
So the picture's just a little bit clearer now. If Weaver is benefiting, it wouldn't be unique to him - other righties with similar deliveries could take advantage, too, and maybe that's what we're seeing with Lackey, Escobar, and Colon's contact rates. It could help home righties, and it could help visiting righties. Weaver seems like he could take particular advantage, and maybe he has. An anonymous Mariners player thinks so. But maybe he hasn't. We can't know. We can only look at numbers.