Helmets and the Law — Law 28.4 and Law 37.4 (2017 Code, 6th Edition)

Under Law 28.4, a batsman's helmet may be placed behind the wicket-keeper while batting, provided it is not actively in the field of play. Under Law 37.4, if the ball strikes a batsman's helmet while it is being worn, it is not out caught.

Source: Law 28.4, Law 37.4, Law 28.3

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