This is offered as a solution a lot, but I am not sure if it would actually be effective. Football helmets were introduce early in the 20th century because dozens of people were dying every year playing football. Football helmets put an end to those deaths caused by acute trauma, but the physics of the game and those collisions haven't changed. Football is just a more violent game than Rugby due to various reasons like position specialization, more frequent stoppages of play, and the inherent directions of play for the offense and defense. It is rare to have two players in rugby running full speed at each other head on. That happens in football on nearly every play and often multiple times per play.