A professional football game is not “normal activity”.
There’s nothing in playing football that would trigger AFib.
AFib is an irregular heartbeat. It either is or isn’t irregular. If it’s not irregular then he can do anything he normally does—anything, including playing football.
AFib is nothing like a heart attack. It’s nothing like a stroke. It’s an irregular heartbeat caused by a mix up in electrical signals. It’s easily corrected by a cardioversion (low energy shocks) which he has had done. This means his heart is beating in regular rhythm and working normally at this point in time.
If he goes back into AFib (an irregular heartbeat) during the game, he’ll know it. He’ll get tired and lightheaded immediately. He can sit out at that point. Or, he can choose to continue to play, because...exercise while in AFib is good for you. It helps prevent blood from pooling. One of the worst things you can do while in AFib is just sit there doing nothing.
He’s in absolutely no physical danger playing football. Absolutely none. The only question is: will his heart be able to pump enough blood to keep up with his physical activity IF it goes into an irregular heartbeat?
It is not certain that he will go into AFib during the game. He may play the entire game and be just fine.
People freaking out because he is playing a football game don’t know what they are talking about.