opportunity to score more runs from this extra ball. Specialist roles The captain is often the most experienced player in the team, certainly the most tactically astute, and can possess any of the main skillsets as a batter, a bowler or a wicket-keeper. Within the Laws, the captain has certain responsibilities in terms of nominating his players to the umpires before the match and ensuring that his players conduct themselves "within the spirit and traditions of the game as well as within the Laws". The wicket-keeper (sometimes called simply the "keeper") is a specialist fielder subject to various rules within the Laws about his equipment and demeanour. He is the only member of the fielding side who can effect a stumping and is the only one permitted to wear gloves and external leg guards. Depending on their primary skills, the other ten players in the team tend to be classified as specialist batters or specialist bowlers. Generally, a team will include five or six specialist batters and four or five specialist bowlers, plus the wicket-keeper. Umpires and scorers The game on the field is regulated by the two umpires, one of whom stands behind the wicket at the bowler's end, the other in a position called "square leg" which is about 15–20 metres away from the batter on strike and in line with the popping crease on which he is taking guard. The umpires have several responsibilities including adjudication on whether a ball has been correctly bowled (i.e., not a no-ball or a wide); when a run is scored; whether a batter is out (the fielding side must first appeal to the umpire, usually with the phrase "How's that?" or "Owzat?"); when intervals start and end; and the suitability of the pitch, field and weather for playing the game. The umpires are authorised to interrupt or even abandon a match due to circumstances likely to endanger the players, such as a damp pitch or deterioration of the light. Off the field in televised matches, there is usually a third umpire who can make decisions on certain incidents with the aid of video evidence. The third umpire is mandatory under the playing conditions for Test and Limited Overs International matches played between two ICC full member countries. These matches also have a match referee whose job is to ensure that play is within the Laws and the spirit of the game.