Can you bring in beer for concerts in the park?

I doubt it

Legally? Well.. I mean you can bring a drink just about anywhere, just as long as the coppers don't see ya, that's why it's good to bring in liquor, mixed with PepsiCola , yes, they didn't care so much when I was your age, but times change ,

No.

If it's sold at an event they are having, normally no.

I am not sure. They may be selling draft beer in the concession tents.