In volleyball, a 'Libero' is a:

In volleyball, the libero is a specialist defensive player who plays only in the back row. The position was introduced by the FIVB (Fédération Internationale de Volleyball) in 1998, and it was first used at a major event at the 1998 World Championships.

Why the libero was introduced:

The FIVB introduced the libero to make rallies longer and more exciting, by improving teams' defence (receiving serves and digging attacks), and to give shorter players a chance to play at the top level.

Rules for the libero:

• The libero wears a jersey of a different colour from the rest of the team, so that referees can easily identify the player.
• The libero can only play in the back row.
• The libero cannot attack (spike) the ball when it is completely above the height of the net.
• The libero cannot block or attempt to block.
• Under FIVB rules, the libero cannot serve.
• If the libero makes an overhead finger pass (set) from the front zone, a team-mate cannot attack the ball above the net.

The libero can replace any back-row player without being counted as a regular substitution. These replacements are unlimited, but there must be a completed rally between two libero replacements.

A team may name two liberos in its squad of up to 14 players, but only one can be on the court at a time.

The libero cannot be the team captain on court.

The word "libero" is Italian for "free", reflecting the player's freedom to come in and out of the game. (In football, "libero" also means a sweeper, a free defender behind the defensive line.)

Other volleyball positions:

• Setter: the playmaker who sets the ball for attackers.
• Outside hitter (wing spiker) and opposite hitter: the main attackers.
• Middle blocker: the player at the centre of the net who blocks and makes quick attacks.

Why not the other options?

• ✗Team captain: the libero cannot be the game captain on court.
• ✗Main attacking player: attackers are outside and opposite hitters; the libero cannot attack above the net.
• ✗Assistant referee: volleyball officials include the first referee, second referee and line judges.