3) excludedness or limitedness
Johan Huizinga's Homo Ludens (1944), p. 13:
Summing up the formal characteristics of play we might call it a free activity standing quite consciously outside "ordinary" life as being "not serious", but at the same time absorbing the player intensely and utterly. It is an activity connected with no material interest, and no profit can be gained by it. It proceeds within its own proper boundaries of time and space according to fixed rules and in an orderly manner. It promotes the formation of social groupings which tend to surround themselves with secrecy and to stress their difference from the common world by disguise or other means.You probably aren't really 'playing' most of the time.
We saw "The Swing" in the Wallace Collection. It's a very interesting piece.