Something I'd like to see on every hard cap league is a cap relief calculation for team drafted players, going up the later that player was drafted. Maybe 5% per found, maybe 7.5%?

So many times teams are basically forced to move on from role players that are fan favorites because it's literally impossible to pay a team of veterans under the cap unless you have no star players and I think it would be genuinely interesting to provide a benefit on the cap side to keeping drafted players in house past their first or second deals. Part of why it's so hard to be a fan is knowing that anyone but the absolute TOP stars are just consistently going to be moving on in a few seasons.

Baseball: There is now a gun under second base.

Sports in general need to make it illegal to dive to draw an undeserved penalty (or actually enforce the existing rules)
Or
They need to decrease the penalty for fighting so it doesn't result in an ejection.

One or the other.

playoff hockey: have referees on the ice that call penalties for rule infractions. playoffs are violent garbage.

Fencing: Allow shields.

Basketball. Same everything, except you have to dribble the ball with your forehead.

NHL Hockey: Goaltenders eligible for contact if handling the puck outside the crease, and outside the trapezoid. Same as any other players.

Thunderdome rules for MMA. Keep going until there is a sub or knock out. No rounds and no time limit.

Baseball: make steroids mandatory