The Extremes of AT&T Park

Yesterday's post had a section filled with shock and awe over the Giants' OPS+ ranking. They were third in the National League with a 100 OPS+. That's good!

But what is OPS+, he asked in his best '50s filmstrip voice? It's a mark that's relative to league average (meaning a 100 mark is exactly average), but it also has to do with park effects. A .250/.310/.400 line might be an 85 OPS+ for a player on the Rockies, but it might be a 110 OPS+ for a player on the Padres.

Park effects can be a little tricky to figure out, but the basic idea is to add up the Giants' and opponents' runs scored in AT&T and compare them to the runs scored by the Giants and their opponents away from AT&T. For years, AT&T played as a slight pitchers' park. Ever so slight. Some years it was a totally neutral park. This year, the park is playing as an extreme, extreme pitchers' park. Really extreme. Drinking Mountain Dew and doing BMX tricks and crap.

If you believe the single-season park effect for 2012, AT&T Park is suppressing runs more than PetCo Park ever has. It's suppressing runs more than the Astrodome ever did. More runs than Safeco ever has. More than Comerica before they moved the fences in. More than Forbes Field, Dodger Stadium, Citi Field ...

The point: If you believe the three-plus months of numbers, AT&T Park this season is playing like one of the most extreme pitchers' parks in baseball history. The one-year park factor at Baseball Reference is 81 for hitters. I went through the Astrodome, PetCo, Dodger Stadium ... couldn't find anything that low in the history of those parks.

All sorts of things can change park factors from year to year. Weather patterns, for example, both in San Francisco and around the country can make a huge difference. To use a simplified example, if it's an unseasonably hot and dry summer in San Francisco, but the Giants visit Wrigley twice with the wind howling in, that would rejigger the numbers slightly in favor of AT&T being something of a hitters' park. That's a dumbed-down example, of course, but I only dumb it down because of my lack of respect for you, the reader.

More importantly, a half-season of park factors is subject to all sorts of statistical noise. It's typical to use three-year rolling averages for park factors to eliminate some of that noise.

But if I'm reading this right -- and I'm probably not! -- the OPS+ and ERA+ numbers for individual players are based on comparisons to a hypothetical league-average player created using the single-season park factor. Which means there are two options:

1. You can believe that AT&T Park is really playing like a hyper-extreme pitchers' park this year. It's certainly possible.

2. You can look at these numbers with skepticism and expect them to bounce back to normal soon.

I'm not saying I know the answer. But I'll lean toward #2. And this is all to say, remember those claims of the Giants having an average offense? Let's chill out on those for a while. The OPS+ numbers behind those claims might have a bunch of three-month park noise behind them.

Another way to put it: If you believe the OPS+, you probably have to look at the ERA+ numbers too. The Giants' ERA+ this season is 100. Again, totally average. And because of the extreme park factors, you get things like this: Madison Bumgarner, 39th-best pitcher in baseball over the last two seasons, just behind Wandy Rodriguez and Justin Masterson.

I'm not ready to believe that. I'm a thinkin' there are sample-size goblins afoot and that the AT&T from the decade before 2011 is the real AT&T. Which would mean the Giants' offense isn't as close to average as we thought, but that Madison Bumgarner is better than his park-adjusted numbers over the last two seasons. You can see how that's a bit of a Sophie's Choice of optimistic trends.

Alright, this was supposed to be a 150-word post that got all dorky. Even worse, it's the kind of dorky that I'm bad with, so I probably screwed everything up. And there weren't even any stupid jokes! Man. As an apology, here is a GIF of Jeffrey Leonard dancing down some stairs.

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