I think what's not that common is people cheating with their partner's best friend, particularly in a sporting team.
Everyone knows that a lot of players mess around - they have ample opportunity to do so.
Every time this sort of thing has come out one or other player has had to go - usually the one that's acted up. The reason is that in any team environment, even one where half the players mess around all the time, the unspoken rule will be "not in your own back yard". Team sport is all about trust, and you can't do anything much more damaging to trust than sleep with a fellow player's wife.