I believe most if not all NFL stadiums have holding cells and probably police substations.
Nope.
Only Veterans Stadium Had an actual cell, as did Lincoln Financial Field, before they did away with the cell for publicity reasons. The remodeled it into a “room”. They still have a real Judge on staff for every home game.
Other stadiums have used already existing rooms to sometimes hold unruly fans until police arrive.
No other NFL team has had the problem to the extent Philadelphia did/does.
I do know, anywhere that has 80,000+ fans, football, NASCAR, Soccer, has a paid police, and emergency staff.