I finally went to a Yankee game. I've been in New York for almost 5 years and never even made it to the old stadium. My first comment was "well, it's bigger than Fenway." It's nice, but I was hoping to happen upon some magical veggie dogs that many other ballparks are sporting. No dice.
I forgot I wasn't having gluten (I remembered not to have beer) when I bought a NY pretzel. It was OK, but didn't really cut the mustard (despite drenching it in mustard.) When lo and behold I stumbled upon the garlic fries. These fries were total vampire killers and were pretty darn tasty. Basically it was just some jarred minced garlic and parsley piled on top of some fries. Still for ballpark fare it was pretty good. Other items that might be vegan, but I didn't ask were PB&J, knish, Cracker Jacks (vegan), potato chips, and nachos without cheese or chili.
Here's a guide to vegetarian options at ballparks nationwide. http://www.soyhappy.org/venue.htm Looks like San Francisco is the place to go. I'll have to go to a Mets game and I hope they bring back the veggie dogs! I also hope they all start getting vegan dogs. How hard can it really be?