Changing the rules of traditional games:

Height Limit Basketball / Weigh Limit American Football.

• Teams have a set total height / weight maximum, and can't have more than that on the floor at any time.
• variants include with / without limits on number of players on the field at any one time.

Continuous Time Basketball / NFL

• The clock never stops (except for delay of game) - make it like soccer.
• 20 min/quarter
• This would basically be the same game, but the end would be a lot smoother

Volleyball with no player limit

• You could have so many players that the ball wouldn't be able to hit the ground
• But they'd get in each other's way quite a bit.
• What is the optimal number of players?

Additive win differential

• no time limit; game is over when one side is winning by N points
• or, you win when you have at least 20 points and are winning by N