The old Yankee Stadium outfield wall is in red; the new one is in blue. Says Rybarczyk:
I created this by using actual prints from the new stadium, and by using high resolution satellite photos for the old stadium. You may have heard that the dimensions at the new park are the same as the old park, but that is not strictly true. In certain spots the distances are the same or similar, but there are significant differences in the fence line. As you can see in the diagram, most of right field is shorter in the new park, by as much as 9 feet, but more typically by 4-5 feet (the blue dotted lines in the corners are scale markings that are 4 feet apart.) In center field, the new park is actually a bit deeper, and in left field, the parks are very similar. From some analysis I’ve done on home runs, these differences would tend to increase home runs overall, and particularly in middle-to-lower power hitters.Note that right field is closer to home plate to begin with, and already had the most homers hit to that part of the field in the old stadium; so moving that wall in closer will surely cause a greater marginal increase on homers hit there than the decrease in homers caused by the left-center wall being moved farther out, where many a fly ball will continue to go to die. And indeed, according to the New York Times, the new Yankee Stadium has seen the most homers per game in the majors so far this season (in an admittedly small sample size of four games).
The fence distances are not the only difference: in a few places, the fence is shorter (particularly the right field corner). A typical conversion factor for fence height to distance is that lowering a fence by 1 foot is roughly equal to moving it 0.84 feet closer to home plate. So, with the right field fence being a couple feet shorter in the new park, this is like moving it in a foot and a half or so.
Looks like good news for lefty sluggers and bad news for the Yankees pitching staff.