NFL

Both teams are allowed to keep one silverback gorilla on their roster and can use it for 1 play during the course of a game

Move the kickoff back to the 30 yard line, but if you kick it through the goal post, you’re awarded a point

On the field goal posts, designate a "right down the middle" section that scores an extra point on field goals (obviously not on extra points, though). make it VAR and easily (and quickly) reviewable.

I'd change how the draft works.

Bottom 8 teams don't get a 1st round pick. 9th worst team picks first and it proceeds as normal. Rounds 3 and 4 are like the first round. Round 2 is where the big changes happen: each of the bottom 8 teams drafts 3 times in snake order. Picks for the 2nd round are protected and can't be traded. Rounds 5+ don't really matter so they either go away or proceed as normal.

So basically the teams that suck the most can't suck their way into a top tier QB, but they get a lot of quality picks to build up a core roster. So it would both discourage tanking for a QB while getting bottom teams help where they need it. Bad teams on the cusp of the 8-9th pick get to engage in game theory. Everyone else gets a slightly better 1st pick, but a slightly worse 2nd and 3rd pick. The best players also get a slightly better chance of getting picked by a competent team to develop them.

Another benefit is bad teams can't count on lucking into a great pick so there's more motivation to be a competent organization because rebuilding your team probably won't happen overnight.

Cons:

No Stroud to the texans or Burrow to the bengals would happen in this scenario. Good teams can't trick bad teams into trading their picks away.

No more punting. You've got four downs and you lose the ball if you can't make it wherever you are. Bring back kickoffs. Team kicking off have to line up 10 yards behind the kicker. Kickoff from the 20. Rest of the team has to start at the 10 can't move until the kicker touches the ball.