A park factor, as used here, is a measure of how a team’s home field changes their statistics. It results from a combination of many factors-the distance and height of the outfield fences, angles, foul territory, visibility, field surface, and weather, to name a few. It is not the case that the Yankees have a high park factor for home runs (PF) because the Yankees hit a lot of home runs. To get a high PF, you need to hit and allow more home runs in your home games than you do in your road games. An average effect on HR is written as ‘100’; a better-than-average park will score something like 120, which means they get a boost 20 percent above average, while a poor hitters’ park would score 90, or 10 percent below average. Players are also graded on who has the best and worst fit to their stadium-not on how well they hit home/road, but how well their profile matches or doesn’t match what the park gives.

New York Yankees and Yankee Stadium 2:
A lot was written early in the season about how much the new Yankee Stadium was increasing home runs, and deservingly so-the new digs were the best home-run park in the majors, with a 125 Park Factor, or 25 percent better than an average (or neutral) PF. Not everything written was accurate, though. Early reporting focused on how well left-handed hitters were doing, describing a “wind tunnel” to right, but right-handed hitters actually benefited more (136) than lefties (117). We saw a drop-off as the year went on, from a remarkable 158 PF in April to an ordinary 97 in September; how much of that was due to some real change (since wind patterns do change with the seasons) or pitchers learning to cope with the new digs, we don’t really know yet. The focus on home runs obscures the fact that it was the absolute worst place in the majors for hitting triples (PF 49) and the second-worst place to hit doubles (80; San Diego had a 77); the net result is that it was a pretty average park for overall run scoring. It does favor sluggers, the more one-dimensional the better, and does not have a strong left/right bias. Hideki Matsui, Jorge Posada, and Alex Rodriguez all had Equivalent Averages about ten points better than their adjusted park-neutral stats, while Derek Jeter, Robinson Cano, and Brett Gardner each lost about five points from the same adjustment. The Tigers who should benefit most would be Miguel Cabrera and Brandon Inge, while Gerald Laird and Adam Everett look least capable. Among the Twins, Justin Morneau, Michael Cuddyer, and Joe Mauer all get about a 10-point gain in EqA; Carlos Gomez, Orlando Cabrera, and Denard Span all take big hits.

Detroit Tigers and Comerica Park:
Comerica was a neutral park overall, with the only noteworthy feature being that it’s a good place for triples (115 PF). That masks a huge split, as right-handed hitters did better than lefties across the board, with better PFs for singles (99/96), doubles (101/92), triples (165/92), home runs (110/88), and Equivalent Runs (112/86).They also had advantages in walks (110/103) and strikeouts (94/107, and in this instance lower means better for the hitter), which all together suggests a visibility problem from the left-hand side of the plate. The difference in EqA made for a 105 PF for righties and 93 for lefties, and was the largest such split in baseball. Curtis Granderson, the Tigers’ only full-time lefty in the lineup, got clobbered by the park this year, not that it did Clete Thomas or Aubrey Huff any favors either; Ryan Raburn, Marcus Thames, and Brandon Inge did very well. As far as potential Yankee effects, Alex Rodriguez should love it, and Derek Jeter should also do well. The rest of the lineup is either left-handed or switch-hits, and will be facing a mostly right-handed staff (the Tigers should make sure Washburn starts on the road), which means they’ll be batting left and suffering for it.

Minnesota Twins and the Metrodome:
The home of the hefty bag rates as one of the league’s better hitting parks, with a mild advantage going to left-handed hitters. Singles and triples are especially elevated, and the stolen-base factor (174) is the highest in the majors. We don’t normally think of steals as something with a strong park effect, beyond the fact that teams tend to run more in low-scoring parks and less in high-scoring parks; since Minnesota is a good run environment that shouldn’t matter. The picture is one that benefits speedy guys most, and the best Twin to fit the park was Denard Span; Cuddyer and Joe Crede were hurt the most. The biggest Yankee beneficiary of what the Metrodome offers should be Brett Gardner, although most Yankees will benefit somewhat. The only real loser is Alex Rodriguez.

Los Angeles Angels of Anaheim and Angel Stadium:
The Big A of A rated as the fourth-best home-run park in the majors this year, at 120; since you don’t expect the weather to cool off as much in LA as elsewhere, that number should stay up in October. Double and triple rates were low, at 92 and 61; the overall effect is to give a small edge to the hitters, and within that, a lean towards right-handed hitters. The differences between the best and worst-fitting hitters wasn’t large-Juan Rivera and Mike Napoli were helped a little more than the rest, while Erick Aybar and Chone Figgins suffered the most, but everyone was within 10 points of the EqA of their park-neutral stats. The Red Sox, meanwhile, are very well constructed to take advantage of the park; Jason Bay, Kevin Youkilis, David Ortiz, and Victor Martinez all fit Anaheim a lot better than they do Fenway.

Boston Red Sox and Fenway Park:
Fenway’s a legend, one dominated by the Green Monster. Contrary to lore, it is actually a neutral to downright poor park for home runs, and worse if you’re left-handed, with left/right home-run Park Factors of 90 and 100. It is also one of the worst places for singles (92), as the short fields let the outfielders play shallow. But it is the best park in baseball for hitting doubles, by a mile (143; Arizona is second at 129). Surprisingly, the Red Sox don’t take particularly good advantage of their park, with Varitek the biggest beneficiary. Jacoby Ellsbury took a big hit, since singles are his whole game. All of the Angels will benefit from playing in Boston, with Kendry Morales getting a big 20-point jump; the Angels’ biggest guns-Vladi Guerrero, Torii Hunter, and Juan Rivera-will get the least advantage from Fenway.

Colorado Rockies and Coors Field:
Coors is the best hitter’s park in baseball, humidor or no. The humidor has the effect of creating a mush ball, and that helps holds home runs down to an average rate, but they can’t do anything about the air. The low pressure that comes from altitude means that pitches don’t move nearly as much as they do in sea-level stadia, which results in the lowest strikeout factor (86) in the majors, as well as one of the highest line-drive factors (118) and lowest pop-up factors (81). Those factors lead to high scores in singles (105, sixth overall), and doubles (117, third), along with the highest Park Factors in baseball for triples (171), batting average (113), on-base percentage (109), slugging (114), Equivalent Average (111), and runs (121). There’s not much of a left/right split, but who needs it? Dexter Fowler, Carlos Gonzalez, and Troy Tulowitzki reaped the biggest benefits, while Garret Atkins and Chris Iannetta got the least; here we’re talking about only getting a 10-point gain for latter guys, versus the 25- to 30-point gains of the better guys. For the Phillies, Shane Victorino and Jimmie Rollins are primed for huge gains, while Jayson Werth hangs back.

Philadelphia Phillies and Citizens Bank Ballpark:
CBP had the third-highest platoon split for favoring right-handed hitters, trailing only Detroit and Texas. That’s coming from the extra-base hits, with double/triple/homer Park Factors of 116/105/116 for the right-handers, and only 97/75/92 from the left, and comes despite the fact that the dimensions are a little shorter to right field than they are to left. Ryan Howard, Raul Ibañez, and Chase Utley emerge as the biggest losers from the configuration, taking roughly seven-point hits to their EqAs; Jayson Werth and Pedro Feliz were the biggest beneficiaries. Look for Tulo and Iannetta to take the biggest advantage, while Gonzalez, Stewart, Smith, and Hawpe suffer.

St. Louis Cardinals and Nu Busch Stadium:
The Cardinals/Dodger series will feature the two best pitching parks in the entire post-season, with each scoring around a 90 PF overall. They are also the only two post-season parks that strongly favor left-handed hitters. The new Busch sits close to the Mississippi River, facing it, and there tends to be a persistent light breeze off the river that kills power hitting; the Cardinals’ PFs for triples and homers are just 71 and 74, the latter making it the third-worst home-run park in baseball. The really amazing thing here is that Albert Pujols had the worst fit of any Cardinal to what the park offered, while Matt Holliday was the second-worst, and yet both hit better at home anyway; Skip Schumaker is the only player who rated as a good fit. The best fit for the Dodgers, in terms of improving himself in Busch, is actually Juan Pierre; right-handed sluggers Casey Blake, Manny Ramirez, and Matt Kemp should fit just as poorly here as they do at home.

Los Angeles Dodgers and Dodger Stadium:
Traditionally one of baseball’s best pitchers’ parks, Dodger Stadium offered up no surprises in 2009. Low walk factors (79, baseball’s worst) and high strikeouts suggest that the visibility isn’t so good; spacious foul territory also gives it one of the majors’ highest pop-up factors (112). The EqA advantage of left-handed hitters (101) over right-handed hitters (90) was the largest in baseball, mainly due to the differences in home runs (114 for lefties, 79 for righties). Right-handed sluggers, like Casey Blake, Manny Ramirez, and Matt Kemp fit the park least well, with Andre Ethier and James Loney matching up best. Like Busch Stadium, Skip Schumaker should take the most advantage of Chavez Ravine, while Pujols and Holliday fare the worst.

A version of this story originally appeared on ESPN Insider Insider.

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You mentioned the weather factor in one place in the article. How much can we figure on the cold suppressing offense, and power hitting in particular? Or is Nate Silver still enforcing his patent on that information/study?
Uh, wouldn't the Twins' park effect on steals be an artificial turf thing?
Despite the seeming fit with Dodger Stadium, Loney turned in a curiously pathetic performance at home (.251/.324/.316) and a much more robust one on the road (.309/.387/.475)
This may already be up on the BP site somewhere, but do we have access to park factors data for all stadia for this season? It would be interesting to see how the non-playoff parks played, too.
That Metrodome stolen base factor is amazing. Has it been anything like that in other seasons?
"The only real loser is Alex Rodriguez."