Yep, fine with a small crowd. But with a big crowd I'll be sitting next to my buddy and he'll have no issues while I'm not getting any data. Having the tower in the park would help, the closer to the tower the better the service, although they need to ramp up the capacity during games.
You can't just "ramp up" capacity during a game. Think of it like this. There is a pizza to provide slices to everyone. If there are four people, the pizza is divided four ways. Increase the number of people to 16, and the pizza is divided 16 ways. The cells at the stadium can handle a certain number of people, and they have tried to evenly distribute as many cells into the stadium as they can. When people start pouring in, the pizza slices get smaller and smaller, and also the amount of noise starts to rise. The more noise, the lower the signal to noise ratio, the worse your phone performs. Same thing happens when trying to jam as many cells as possible into a small area, eventually they all cause noise to each other.
Big crowds and heavy data volume suck.