I never follow baseball, but I am well familiar with that park. Now, this was many years ago, but when I was a teenager, one of my brothers rented an ice cream truck and would park it outside of the park. Quite a few people would buy ice cream before heading inside to the game.
My brother (who was about 18 at the time) didn't have any sort of city vendor's permit to sell there, so we often would have to sell quick, and move quick when the patrol officer headed in our direction.
(He'd move the truck around about 3-4 times during the game.)
Some of the other vendors had a permit; while some others (without permits) did the cat and mouse routine like us. Lastly, we heard (anecdotally) that there were also some, without permits, that "donated" a few dollars and/or food, to the patrol cop who would somehow not notice that the vendor did not display a permit.
Hee hee, it was the pulse of the city back then, sort of a street code/vibe thing. There were no secrets. (Nowadays, that area is pretty much locked down in enforced regulations for all outside independent vendors.)