International Institute of Cricket Umpiring & Scoring
Caught in helmet
"Whilst umpiring a recent Sunday friendly a ball top edged by the batsman lodged in the wicket-keeper's helmet. The fielding side claimed out, but, being completely unsure and feeling that giving out was not correct, I called 'dead ball'. As the fielders were equally unsure they accepted amicably, but naturally this caused much debate in the post-match analysis in the pub. Please advise."Your instincts were correct; the ball becomes dead on lodging in a protective helmet worn by a member of the fielding side. Strictly speaking there is no need to call and signal Dead ball (see Laws 23.1 and 23.3), but the Law allows you to do so if you feel you need to let the players know what is going on. As the ball is dead there can be no dismissal.
It might be worth pointing out that, if the ball had simply hits the wicket-keeper's helmet rather than lodges in it, the striker cannot be out Stumped (Law 39.2). Additionally, if the ball touches a helmet worn by any fielder (and that includes the wicket-keeper) the striker cannot be out Caught (Law 32.3). However, in each case the ball remains in play and either batsman could be out Run out or in several other ways permitted by the Laws.
Read more about Law 23 (Dead ball) at the MCC website