What severity, frequency of football injuries is acceptable?

Clearly, we have not exceeded what we as a society regard as a tolerable level of concussions and torn knee ligaments.

But how much worse would it have to get before talk of banning the sport grew louder?

A case could be made that the people who run football programs are more safety-conscious than ever. But is that enough?

Or is it nonsense to imagine a virtually risk-free version of football, and would we even want that?