Mixed-sex sports are individual and team sports whose participants are not of a single sex. In many organised sports settings, rules dictate an equal number of people of each sex in a team. Usually, the main purpose of these rules are to account for physiological sex differences. Mixed-sex sports in informal settings are typically groups of neighbours, friends or family playing without regard to the sex of the participants. Mixed-sex play is also common in youth sports as before puberty and adolescence, sport-relevant sex differences affect performance far less.