Jack “the Assassin” Tatum and his cohort George Atkinson, who allegedly taught Jack the now infamous “Tatum Hook”, were a pair of the most vicious hard hitting safeties to ever roam a football field, during the early seventies.
In a preseason game Tatum and New England receiver Darryl Stingley collided. Stingley lowered his helmet to protect himself and hit Tatum's shoulder pad. The force of the hit fractured two vertebrae in his neck and severely damaged his spinal cord, leaving him a quadriplegic.
Darryl’s transgression? He dared to run a crossing pattern into Tatum’s zone in PRESEASON.
The NFL later banned all forearms (the Tatum Hook rule) to the heads of receivers because of Tatum’s reputation and this hit. Even though he never used his forearm, no penalty flags were thrown, and Tatum was never disciplined for the play.
I think the NFL’s rules as they are now would preclude any defense, or defensive player for that matter, from coming close to how violent and “physical”, they played the game in the ‘60s and ‘70s…