People dont seem to know the difference between Halacha and Hashkafa.
Most of the people I saw at the game were Yeshivish (Not even MO) but I dont think ive ever saw Chassidim at a Mets game (Maybe they are Yankee fans and go there , I dont know)
Certainly If I saw Rav Sheinberg at a Baseball game I would be taken a little aback, but for a normal person not really.
One is not Allowed to Daven in a place of Tumah, and as DHocker said, He saw 4 Minyanim there (There might have been more) Ive seen Minyanim at the game, In fact Ive even seen Minyanim in the stands.
DJ Hockers numbers are probably more correct than mine as I was mostly at field level where the tickets were higher priced
If your Hashkafa is not to go, that is fine and nobody is forcing you to go, but dont claim its ASSUR or anything. It is ASSUR to declare something ASSUR when in fact it Muttar.
But of course you are free to take a personal vow not to go.