As you know, when creating a match, users have the option to choose whether or not the match is ranked or not:
I believe there should be another option to make the match a custom map. My reasoning behind this is that in custom matches, neither kills nor deaths are added to the user's profile, which makes the map good for training with friends without influencing stats. Another reason is so that players can play approved maps with the old low physics, since this is allowed in custom maps.
Ideas and feedback are welcomed.