Laws of Cricket 1947 Code (Second Edition) - Law 43
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. Should the Wicket-keeper contravene this Law, the Striker shall not be out except under Laws 36, 37, 40 and 41 and then only subject to [Law 46].
Note on Law 43
- This Law is provided to secure to the striker his right to play the ball and to guard his wicket without interference from the wicket-keeper. The striker may not be penalised if in the legitimate defence of his wicket he interferes with the wicket-keeper except as provided for in Law 37, Note 2.
Reproduction of the Laws of Cricket is by kind permission of Marylebone Cricket Club