So this is cool.
It is a tool that allows you to overlay a player's balls in play (or a pitcher's BIP allowed) from their home park and overlay it over any other park in baseball. It's a fun tool, but it's rough. It doesn't adjust for the weather conditions at the time of the play, nor does it make any allowance for fence heights, which is pretty important. So it's fun, if not necessarily the end-all of debate.
Still, if you're curious how Curtis Granderson would have done in Yankee Stadium II last season, just pop in the parks and go:
That's as many as six home runs (depending on how you look at the balls against the wall), including two that were flyouts, with zero homers taken away. Anything yellow to red is an out; anything shaded blue is a hit, the darker the better. As THT notes, Granderson could have had 40-plus homers last season in a Yankee uni if all these balls had the right trajectory.
How about one of the Sox' newest acquisitions? Say, Mike Cameron?
Could Cameron be set up for a big year? That's four flyouts and a line out turned at least into wallballs by the Monster, depending on their trajectory, plus six doubles that may have been home runs in Fenway, plus four more flyouts that are right up against the wall. That's 15 non-home runs fielded beyond the dimensions of the Fenway Park walls.
You can also get a sense of just how cozy some parks are compared to others. Take Adrian Beltre's former home ball park, Safeco, and overlay all balls in play there over the Fenway dimensions.
I count no more than three balls — all in the right-field corner — that would have been hits in Safeco but outs at Fenway. Otherwise, not only is every Safeco home run easily a Fenway home run (absent those screaming liners off the top of the Monster), but there are dozens of outs that turn into hits and homers. And that doesn't even account for Safeco's ability to increase strikeouts and suppress walks (hitting background and all that). It's just not a fun place to hit.
As for Beltre himself, he had only eight home runs last year, split evenly between home and the road, but here is his chart:
There's an obvious double that turns into a homer in right, an out that turns into at least a Wall ball in left, plus four other doubles that either hit or top the Monster, plus three more outs right against it that might be outs — or could be home runs or anything in between, depending on the trajectory. It would be great if this worked back to previous seasons, when Beltre was healthier, but it's not like this is statistical gospel anyway.
Finally, you can look at pitchers' spray charts, as well. How would they do in their cozier confines? Javier Vasquez:
And John Lackey: