Libero substitutes are unrestricted and do not count as substitutions. Except when the libero on the court will be the next server, there must be at least one rally between substitutions involving the libero. If a team uses two liberos, only one libero may be on the floor at the same time in USAV. A player can be substituted out for any reason during their service time. A libero may also be substituted if the coach feels that it is necessary to have another player contribute to the game. There are no rules regarding how long a libero should stay in the game. Coaches tend to substitute liberos after each rally so they can keep their attention focused on the action on the court instead of having to remember who is serving next. Liberos are free to leave the court at any time if they feel like it has become too difficult or uncomfortable playing with only one player on the floor. They can also be replaced by a coach if he or she wishes to have another player contribute to the game. A libero cannot score or dish out points in any way. Their job is simply to defend against balls hit towards the basket by the opposing team's players and throw out help defense opportunities if needed. A libero can use all-fours position to block shots but cannot touch the ball with their hands unless the shot goes up. A libero does not have to be a female player to replace a male counterpart on the court.