With 2 incidents this week involving fan douchebaggery at Phillies games, it called to mind 2 examples in football where the players policed the situation themselves. No tasers necessary. Maybe this is why you see less examples of fans running on the field in football.

Former Colts LB Mike Curtis tackling a fan running with the ball:

 

Steelers Pro Bowl LB James Harrison body slams a fan:
 

 
Of course if you really needed to get on the field, a creative disguise is probably the most effective way.