The members of a team who are scheduled to play a game.  [PJC]

 The formation of football players before the start or a restart of play.  [PJC]

 a list of batters in the order in which they will bat.  [WordNet 1.5]

 any arrangement of persons (rarely, of things), esp. when having a common purpose or sentiment; as, the line-up at a ticket-office window; the line-up of political factions.  [PJC]

 A group of persons including a suspect in a police investigation, arranged so as to be observed by a witness, who is requested to identify the perpetrator, if he/she is present in the group. Such an identification may be used as evidence of guilt of the suspect. Also called a police lineup.  [PJC]