Ball is dead

a) The ball becomes dead when

i) it is finally settled in the hands of the wicket-keeper or the bowler.
ii) a boundary is scored. See Law 19.3 (Scoring a boundary).
iii) a batsman is dismissed.
iv) whether played or not it becomes trapped between the bat and person of a batsman or between items of his clothing or equipment.
v) whether played or not it lodges in the clothing or equipment of a batsman or the clothing of an umpire.
vi) it lodges in a protective helmet worn by a member of the fielding side.
vii) there is a contravention of either of Laws 41.2 (Fielding the ball) or
41.3 (Protective helmets belonging to the fielding side).
viii) there is an award of penalty runs under Law 2.6 (Player returning without permission).
ix) Lost ball is called. See Law 20 (Lost ball).
x) the umpire calls Over or Time.

a) When the ball has become dead under 1 above, the bowler's end umpire may call Dead ball, if it is necessary to inform the players.

b) Either umpire shall call and signal Dead ball when

i) he intervenes in a case of unfair play.
ii) a serious injury to a player or umpire occurs.
iii) he leaves his normal position for consultation.
iv) one or both bails fall from the striker's wicket before he has the opportunity of playing the ball.
v) he is satisfied that for an adequate reason the striker is not ready for the delivery of the ball and, if the ball is delivered, makes no attempt to play it.
vi) the striker is distracted by any noise or movement or in any other way while he is preparing to receive or receiving a delivery. This shall apply whether the source of the distraction is within the game or outside it. Note, however, the provisions of Law 42.4 (Deliberate attempt to distract the striker). The ball shall not count as one of the over.

vii) the bowler drops the ball accidentally before delivery.

viii) the ball does not leave the bowler's hand for any reason other than an attempt to run out the non-striker before entering his delivery stride. See Law 42.15 (Bowler attempting to run out non-striker before delivery).

ix) he is required to do so under any of the Laws.

Ball ceases to be dead

The ball ceases to be dead - that is, it comes into play - when the bowler starts his run up or, if he has no run up, his bowling action.