later in the season when you start getting Saturday games. That leaves Friday night and Saturday for most fans to see a game before "are you ready for some football Sunday." People can time manage, it's really not an either or type of situation. For those that can't see it early it might have a slight effect but you have to remember that the football season is four months long and that doesn't stop blockbusters from happening. Playoffs can have some effect but studios tend not to open movies targeting males, espicially young males during this time period. But even if they did football games don't suck up the entire weekend for most males.
Or you could look at it as honey we should go to a movie, hoping that she/he will leave you in peace on Sunday. :)-