How could Notre Dame possibly allow Sean Astin (in the movie Rudy) to play a down on their field?

I understand Rudy is an emotional and magical movie for football fans but I’m having trouble understanding how Sean Astin was able to play one down in a real college football game? He is an actor – not an athlete. Was Notre Dame the least bit concerned he could have gotten hurt? How about the real practice squad players? Weren’t they upset an actor got to play a down of football and they did not?