Laws of Cricket 1980 Code - Law 40
1. Position of Wicket-Keeper
The wicket-keeper shall remain wholly behind the wicket until a ball delivered by the bowler touches the bat or person of the striker, or passes the wicket, or until the striker attempts a run. In the event of the wicket-keeper contravening this Law, the umpire at the striker's end shall call and signal "no ball" at the instant of delivery or as soon as possible thereafter.
2. Restriction on Actions of the Wicket-Keeper
If the wicket-keeper interferes with the striker's right to play the ball and to guard his wicket, the striker shall not be out, except under Laws 33 (Handled the Ball), Law 34 (Hit the Ball Twice), Law 37 (Obstructing the Field) and Law 38 (Run Out).
3. Interference with the Wicket-Keeper by the Striker
If in the legitimate defence of his wicket, the striker interferes with the wicket-keeper, he shall not be out, except as provided for in Law 37.2 (Obstructing a Ball from Being Caught).
Reproduction of the Laws of Cricket is by kind permission of Marylebone Cricket Club