The rules of cricket
Law 28 (The wicket is down)
1. Wicket put down
(a) The wicket is put down if a bail is completely removed from the top of the stumps, or a stump is struck out of the ground by
(i) the ball.
(ii) the striker's bat, whether he is holding it or has let go of it.
(iii) the striker's person or by any part of his clothing or equipment becoming detached from his person.
(iv) a fielder, with his hand or arm, providing that the ball is held in the hand or hands so used, or in the hand of the arm so used.
The wicket is also put down if a fielder pulls a stump out of the ground in the same manner.
(b) The disturbance of a bail, whether temporary or not, shall not constitute its complete removal from the top of the stumps, but if a bail in falling lodges between two of the stumps this shall be regarded as complete removal.
2. One bail off
If one bail is off, it shall be sufficient for the purpose of putting the wicket down to remove the remaining bail, or to strike or pull any of the three stumps out of the ground, in any of the ways stated in 1 above.
3. Remaking the wicket
If the wicket is broken or put down while the ball is in play, the umpire shall not remake the wicket until the ball is dead. See Law 23 (Dead ball). Any fielder, however, may
(i) replace a bail or bails on top of the stumps.
(ii) put back one or more stumps into the ground where the wicket originally stood.
4. Dispensing with bails
If the umpires have agreed to dispense with bails, in accordance with Law 8.5 (Dispensing with bails), the decision as to whether the wicket has been put down is one for the umpire concerned to decide.
(a) After a decision to play without bails, the wicket has been put down if the umpire concerned is satisfied that the wicket has been struck by the ball, by the striker's bat, person, or items of his clothing or equipment separated from his person as described in 1(a)(ii) or 1(a)(iii) above, or by a fielder with the hand holding the ball or with the arm of the hand holding the ball.
(b) If the wicket has already been broken or put down, (a) above shall apply to any stump or stumps still in the ground. Any fielder may replace a stump or stumps, in accordance with 3 above, in order to have an opportunity of putting the wicket down.