Putting your head down is kind of how your body naturally protects your eyes and vital organs from impact.
To me its like trying to tell a shark not to roll its eyes back when it attacks... Eons of natural selection has perfected this reflex... Shazier's injury, as awful as it was, is just
another "wrong place, wrong time" event we have to face sometimes... He was trying to hit a moving target, and something went wrong.