We'd just have to make sure we have skilled judges who can make the call if it is handled realistically. If someone gets mad they can't one hit ko with a single swift punch then they will lose the match by the judges call unless they can get their act together.

Edit: for who reacts quicker, generally the advantage would go to the person doing the attack, being quicker to act then react

Edit: for unofficial matches, you can allow the other person to have a weapon such as a shinai if they practice kendo, for example.