What rule would you change or bring in?
Try keep it to do with the playing of a match on-field and preferably simple.
I considered tv referee and red for diving but
I'd introduce a kick in instead of a throw in.
Reason
1. Imo, a throw in is usually not an advantageous position to restart a match
2. Would discourage the hoof and encourage good football, keeping the ball in play.
Disadvantages.
1. Could do the opposite and actually slow the game down as a 'kick-in' in the oppositions half is essentially a set piece which teams would take ages to organise.
2. Might be considered too drastic.