My number one pet peeve about modern football is professional fouling. It breaks the flow of matches, favors the defensive side over the attacking, and robs us of some memorable break-away goals. A yellow card is too soft a penalty for it imho.
A red card would be too much. Also because it'll make for too many judgement calls from the ref, given how big an impact a red card has (and it'll make VAR even more of a hellscape). Instead introduce an orange card, which is a sending off for, say, 15 minutes (and with less than 10 minutes to go, then two players off).To be clear for fouls, where the player is breaking up a promising counter without having any chance of getting to the ball, be it pulling back the opposition player or sweeping their legs.
The negative would be player safety as I could easily see players stretching extra hard in a dangerous to get near the ball, while knowing full well they're ever only getting the man. Still, I'd take that, and trust the refs to make the right calls in those spots.