Sporting events are pretty easy to get into, the key is to have a prop and act like you belong.
I once got into a NHL playoff game by picking up a plastic beer cup off the ground in the smoking area outside of the arena and just walking in through the door. They had a security guard standing there with one of those UV stamp checkers. I showed my hand, he scanned, there was nothing there and I just keep walking like nothing and he didn't say anything.
The hard part is getting a seat in a sold out event... If you don't mind standing, there are plenty of places to stand and watch.
I'm an amateur photographer (did weddings part-time), but bring my camera bag everywhere. I'll walk up to a security guard and ask him for directions to the press area, making sure that my camera is decked out (DSLR with battery grip, flash, and huge lens).
I haven't had the balls to try at the NFL level, but it works fine at the collegiate / city level depending on the size of the game.
This form of social engineering is acting like you belong and that you know what you're doing.
I understand the general principle of how this works, but how are things like press cards dealt with? It seems like that's a major signal that you aren't part of the in-group.
This starts going down the rabbit hole, but you can misrepresent yourself as shooting for <small newspaper / blog / group> and say there were communication problems.
Other times there are multiple entrances and if security doesn't communicate with each other you can try again.
It all depends on how willing you are to push the boundaries.
I once got into a NHL playoff game by picking up a plastic beer cup off the ground in the smoking area outside of the arena and just walking in through the door. They had a security guard standing there with one of those UV stamp checkers. I showed my hand, he scanned, there was nothing there and I just keep walking like nothing and he didn't say anything.
The hard part is getting a seat in a sold out event... If you don't mind standing, there are plenty of places to stand and watch.