Fox made two coaching mistakes that were HUGE and cost the team the game.
1. With one first down, Denver ices the game. Sure, it's 3rd and 7 or 8, but you don't run the ball there when you have Manning as your QB. You went out to get him to make plays to win games - call your best medium distance pass play and let him put the ball on the receiver's hands to get the first down and win the game.
2. With 31 seconds left and two time outs, you can work the middle of the field. You only need a field goal, and again, you have Manning as your QB. You do not kneel on it.
What is really funny is the Falcons are behind by one the next day and Matt Ryan manages to use his two timeouts and 34 seconds to get his team into position for the win, but Fox thought a sure fire HOF QB couldn't get it done for Denver? Absurd.
Manning is easily the best QB of his era in terms of making plays no one else can make. What Fox did was to make Denver's decision to get Manning a moot point. He handicapped his team in a way that almost makes me question if he wasn't paid off.