Yankee Stadium a Pitcher’s Park?

It didn’t take long for criticism to rain down on the new Yankee Stadium last season. From fans pining for the mystique and aura of the old stadium, which was still standing across the street, to the pundits who claimed it more a mall than a ballpark, everyone had an opinion about what was wrong with the park. But a few games into the 2009 season, another issue emerged: Baseballs were leaving the park at an alarming rate. The effect seemed so pronounced, in fact, that commentators came up with a new name for the Stadium: Coors Field East.

Through the season’s first two months the park lived up to the moniker. The Yankees came to bat 921 times during that span and hit 45 home runs, or one every 20.5 plate appearances (PA). Opponents didn’t have quite as much success, hitting 42 home runs in 983 PA, one every 23.4 PA. That was still far ahead of the AL pace for those two months, a home run every 35.2 PA. The Yankees claimed that the new stadium’s dimenions were identical to the old (though a few sources disputed that notion). But something appeared to be a bit different at the new park.

Two months represents a small sample, especially regarding park data. Park factors are most accurate when using a three-year sample, so a two-month sample might mean nothing. To that end, the stadium experienced a statistical correction in June. While the Yankees hit home runs at a slightly less rapid pace, one every 22.3 PA, their opponents saw a precipitous drop, hitting a home run once every 41.8 PA. Opponents never got close to their early-season marks, hitting a home run every 37.7 PA from June through season’s end. The Yankees hit a home run every 24.8 PA from June through September, a bit lower than their April and May pace.

Yankees	PA	HR	PA/HR	Opp.PA	Opp.HR	Opp. PA/HR
April	298	15	19.87	311	13	23.92
May	623	30	20.77	672	29	23.17
June	490	22	22.27	502	12	41.83
July	604	24	25.17	603	16	37.69
August	539	26	20.73	517	15	34.47
Sept	623	19	32.79	603	16	37.69
Total	3177	136	23.36	3208	101	31.76

There is no doubt that the Yankees benefitted from their new park, though that appears to be by design. The lineup featured not only three lefties, but also four switch hitters. Each of those four switch hitters has displayed more power from the left side over his career, and each also exceeded his career power numbers from the left side in 2009. After losing two lefties this off-season, the Yankees added three to their starting lineup, so perhaps we will see a similar effect this season.

But despite all those home runs, Yankee Stadium actually leaned towards being a pitchers’ park, according to ESPN’s Park Factors. While it ranked first in HR factor, it ranked second to last in doubles, with only Petco Park — considered the most cavernous park in the league — more heavily suppressing doubles. But, again, all of this uses just one year’s worth of data. In order to get a better read on how the park plays we need to study it over multiple seasons. As we saw in April and May, a few months of aberrant production can skew a season’s worth of numbers.