the same as any delivery, to get a wicket. The bowlers either target the wicket directly or they try to force an awkward shot out of the batsman in order that a fielder may catch it a "bouncer" is the latter. Bowler v Batsman is a brutal duel in cricket. In the past it has been a tactic to actually target the batsman to force a defence, eg "bodyline" bowling. Yes it was a bouncer that was the cause, it hit him in the neck, presumably unprotected by the helmet. Very sad and thankfully rare in cricket. This will no doubt induce a new helmet design.