Both, what we do for our team, which seems to work, is condition, and then do something that takes a lot of mental focus. That way you can work on your mental focus while you are fatigued. It is easy to be focused when you are in a practice bubble nad you are loose and you have barely broken sweat...but when you just ran a bunch of sprints, pushups, squat jumps etc. and then you are asked where you throw the ball when the #1 receiver is caught up in a jam and the slot guy is running a post which is being carried by a linebacker, it is a challenge.
That is where it is the coaches fault ^^ get them ready.
It is the players fault for not practicing like it is a game. Games are won monday through saturday. Sunday just displays what kind of money was put in the bank monday through saturday. Players should practice every rep as if it was a game situation and when watching film put themselves in the film etc.