When players are substituted during play, it is called changing on the fly.

A player could be substituted for any reason (not just if he was injured and unable to continue).

A player may only be substituted during a stoppage in play and with the permission of the referee.

A player who has been sent off (red card) may not be substituted; the team will have to make do with the remaining players.

During a 20-second timeout, only one player may be substituted.

Bandy: A red card indicates a player has been excluded for the remainder of the match and cannot be substituted.

Canoe polo: A red card indicates a player has been sent off for the remainder of the match and cannot be substituted.

The player cannot take any further part in the game and cannot be substituted.

If an expelled player cannot be legally substituted, the opponent wins the set.

A player may be substituted for tactical reasons or to replace an injured player.