Laws of Cricket 1947 Code (Fourth Edition) - Law 31
The wicket shall be held to be "Down" if either the ball or the Striker's bat or person completely removes either bail from the top of the stumps, or, if both bails be off, strikes a stump out of the ground. Any player may use his hand or arm to put the wicket down, or, even should the bails be previously off, may pull up a stump, provided always that the ball is held in the hand or hands so used.
Notes on Law 31
1. A wicket is not "down" merely on account of the disturbance of a bail, but it is "down" if a bail in falling from the wicket lodges between two of the stumps.
2. If one bail is off, it is sufficient for the purpose of this Law to dislodge the remaining one in any of the ways stated or to strike any of the three stumps out of the ground.
3. If, owing to the strength of the wind, the captains have agreed to dispense with the use of bails (see Law 8, Note 2), the decision as to when a wicket is "down" is one for the umpires to decide on the facts before them. In such circumstances the wicket would be held to be "down" even though a stump has not been struck out of the ground.
4. If the wicket is broken while the ball is in play, it is not the umpire's duty to remake the wicket until the ball has become "dead". A fieldsman, however, may remake the wicket in such circumstances.
5. For the purpose of this and other Laws, the term "person" includes a player's dress and equipment as defined in Law 25, Note 4.
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