The difficult part of this question is what is meant by "safe." Does safe mean that no players ever get concussions or that, say, fewer than 15% get concussed? Would soccer or hockey meet such a stringent standard?
We should face the fact that a significant part of football's appeal is the violence that's inherent to the game. Why else would one out of six Americans want to watch a 40-year-old boxer punch a 29-year-old MMA fighter? If violence were not important then the NFL could convert to two-hand touch football and suffer no loss in popularity.
Bottom line: The question is how much concussing is acceptable? It seems that this question is best answered by the NFL Players Association, with the understanding that the more dangerous it is to play football, the greater the compensation and the greater the health benefits must be. That is, there is a marketplace negotiation in which the players receive recompense (or battle pay) for the physical risks that they assume.
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