Who is a runner?
A player who runs for a batsman who is injured or ill and cannot run for himself is referred to as a runner. Such an injury or illness to a batsman should have occurred after the nomination of players for that particular game. A player carrying an injury or illness from before the nomination of players is not allowed a runner.
What conditions does a player have to fulfill to run for a batsman?
The player acting as a runner for a batsman has to be a member of the batting side and, if possible, should have already batted in that innings. The runner has to wear external protective equipment equivalent to that worn by the batsman for whom he runs, and has to carry a bat.
Where does the runner position himself? When the batsman the runner is running for is on strike, the runner has to stand in the crease at point or square leg, according to instructions from the square-leg umpire. When the batsman is not on strike, the runner takes the crease at the non-striker's end, and the batsman can stand at point or square leg.
Both batsmen can have runners at the same time, which would mean two players at the wicket and two standing parallel.
What rules apply for dismissals when runners are in action?
Both the runner and his batsman have to be in the crease when the ball is in play, or risk being stumped or run out.
The batsman can be dismissed even if the runner has made his ground but the batsman is himself out of his ground.
If the runner is out of his ground when the ball is in play, the batsman stands the risk of being run out or stumped according to the normal law, even if the batsman himself is in his ground. This applies to stumpings too, only the mode of dismissal becomes "run out", as happened recently in the Under-19 World Cup final when Saurabh Tiwary of India, the striker, was in his crease but his runner, Tanmay Srivastava, had moved out of the crease. Bradley Barnes, the alert South African keeper, put the wicket down and Tiwary was ruled run out.
What other rules apply?
The batsman suffers the penalty for any infringement of any other law by his runner as if the batsman were himself responsible for the infringement. For example, if the runner is found guilty of handling the ball or obstructing the field, the batsman is deemed out. Conversely, when the batsman is not on strike, he can be dismissed handling the ball or obstructing the field.