What is "pick-up game"

n. (context sports English) An impromptu game that is spontaneously started by a group of players.

In sports, a pick-up game is a game that has been spontaneously started by a group of players. Players are generally invited to show up beforehand, but unlike exhibition games there is no sense of obligation or commitment to play. Pick-up games usually lack officials and referees, which makes them more disorganized and less structured than regular games but the total number of players in such games globally is likely to be greater than the number playing in formal competitions and leagues.

Without formal rules and regulations, pick-up games are often played with a less rigid set of rules.