I thought I would try to capture a few things I find, with regards to house rules from the various posts here, at BGG and other places.
1 - From neilpat's solitaire league
I plan on playing out my 8-team solitaire league with each team playing each other once. I have not broken any published game rules and my random selection of three defensive players after the offense selects a play retains objectivity as far as I can tell.
After eleven games, teams have been averaging 19.2 points per game. I think that is realistic given the defenses of the teams involved and the fact that I have had the home team just run out the clock and not attempt to score in the ninth round if the home team leads and the game outcome has been decided.
One thing I would like you to consider as a "Hail Mary" option is to allow a trailing team to convert one of their field goal playbook cards to a touchdown card if they trail by 4 or more in the last round and they hold no touchdown cards. Such a conversion would be penalized an appropriate number of rating points (perhaps -5?). One example of why that that might be needed was my most recent game when Seattle trailed San Fran 14-10 on their last scoring turn and Seattle held four field goal playbook cards. It made no sense for Seattle to attempt a field goal in that situation and yet that was their only option.