If i want to go to the game that started 20 minutes ago and need a single ticket to get in, how can i go about it?

Buy one at the box office or from a scalper on the street.

Plenty of people sell tickets around the stadium.

Find the dude on the corner with the cash selling tickets he says he wants to buy tickets for this part of this can he's really selling tickets

Scalpers

There may be some out there selling tickets! Bring cash. That will be your best bet.

Yep a corner dude.