AKA: Musical Crash or Clump
Players mingle or dance around a space. Constantly moving until the leader shouts out a number. All players must then try to get into groups of that number. Any group/s that don’t succeed are out.
Can be played to music, so that when the music stops players have to get into groups.
An alternative is for players to find others who have things in common, such as the same shoe size, age, eye colour, hair colour, etc.
See Shipwreck for a slightly more complex version