Petco Park has a well-earned rep as a pitchers' mecca. Does that diminish Jake Peavy's start?

	Petco's vast dimensions make it baseball's second-worst hitters' park, after RFK Stadium. John W. McDonough/SI

By Joe Sheehan

Jake Peavy is one of the top starters in the National League, and he would be in any ballpark. However, the Padres' ace -- and all pitchers -- benefit from the generous dimensions of Petco Park. Since opening in 2004, Petco has established itself as the second-best yard in the majors for pitchers, trailing only RFK Stadium in Washington, D.C.

Among the variables that Baseball Prospectus employs to measure a pitcher's effectiveness is park factor, which is determined by comparing the number of runs scored in games played at a team's home park with the runs scored in that team's road games. Petco's park factor is 944 on a scale in which any number higher than 1,000 reflects an above-average environment for run scoring. The 944 score means, simply, that Petco Park, over the last three years, has reduced run scoring by 5.6% compared with the average stadium. The following are the five friendliest ballparks for pitchers and the five most hostile, with their park factor in parentheses:

BEST PITCHERS' PARKS
RFK Stadium, Washington (935)
Petco Park, San Diego (944)
Shea Stadium, New York (955)
Busch Stadium, St. Louis (960)
AT&T Park, San Francisco (972)

WORST PITCHERS' PARKS
Coors Field, Colorado (1,143)
Chase Field, Arizona (1,063)
U.S. Cellular Field, Chicago (1,043)
Rogers Centre, Toronto (1,036)
Rangers Ballpark, Texas (1,029)

Why does a park play a certain way? Altitude, the distance of the outfield fences, the amount of foul territory and the weather are the biggest influences. In the case of Petco the game's deepest gaps (401 feet to left center, 400 to right center) make hitting homers tougher (5.9% fewer than the average, tied for sixth hardest). The stadium is at sea level, and the Pacific winds neither push balls over those distant fences nor into those gaps for doubles (at 6.6% below average, it is baseball's toughest park for doubles).

What does this all mean for Peavy? Even if you adjust his ERA based on his home field by raising it 2.8%, or half of Petco's park factor, he has, at week's end, a Gibsonesque 1.73 ERA, which is still, by far, the lowest in the NL. His ERA may be slightly lower than it would be in a neutral environment, but the relative value of his performance is second to none.