What happened here, though, has very little to do with a helmet: it is impossible to design one which both protects the head completely and does not limit the batsman's mobility. This ball went behind the helmet, finding a gap in the armour offered by the body and the helmet.
The result was something those of us who played before all this armour became commonplace were quite familiar with: you never turned your back on the ball, because it could still hit you and you needed to be able to watch it to see what it was doing. And since you were watching it, you might as well do so positively, by punishing that kind of gift, which wasn't threatening your wicket in any way, by using its speed to help it on its way handsomely. That seems to have been forgotten, and if you forget a lesson learned the hard way, you're condemning yourself to relearn it just as hard. Which I think is what just happened.

I said at the start of this posting it has very little to do with a helmet. That means to say it does not have nothing at all to do with it, there is a slight question in my mind whether batsmen have started turning their backs to aggressive bowling. It's of a piece with Boycott's frustratingly cautious batting, which has disappeared with the shorter forms of game. Has the helmet gone too far? Should they be limited, and bouncers correspondingly? It would encourage facing the ball. Why? Because as of a day ago, one bowler is bitterly regretting the bouncer he bowled, and that's one bowler too many. However much he is backed with the reassurances of his colleagues, every evening he faces himself in the mirror knowing that without intending to, he killed. It is a reality which can never go away, and that must colour the use of the tactic for the foreseeable future.