a baseball player on the team at bat who is on base (or attempting to reach a base)

a player from the batting team who literally runs for an injured batsman

A player who is called upon by a batsman who might otherwise need to retire hurt. He is required to wear the same padding and stands at square leg or the non-striker's end to perform the duty of running between the wickets. Often the cause of endless confusion and inevitable run-outs

A player dressed in full batting equipment called to act as the runner for an injured batsman. A runner is only permitted to run for the injured batsman, who is still required to face the bowling.

In cricket, a runner is a team member who runs between the wickets for an injured batsman.