Playing in the NFL is still terribly dangerous, with concussions which lead to brain damage likely the worst effect on players. Several NFL rules have increases the safety of the game. I list these as a fan for 50 years, who has watched thousands of plays and seen scores of injuries and not as a doctor, or someone privy to league injury data.
Here are the most important
1. In 1943, the NFL made it mandatory for players to wear helmets.The league has made a point of publicizing how improvements in the helmet over time has helped players
2. In 1976, the NFL outlawed facemask tackles along with headbutting, and spearing. As Bioethics pointed out, that has not entirely solved the problem:
A downward trend for deaths and for head and neck injuries is attributed to 1976 bans on head butting and spear and facemask tackles. However, these illegal tactics persisted despite bans.
3. The ban of “roughing the kicker” goes back to 1917. According to Sports Charts, the current rule is:
A penalty called when a defensive player makes significant contact with a kicker or punter who has just made a kick attempt. No contact is allowed with a kicker unless the kick has been tipped or blocked by the defense. The offense is awarded fifteen yards and an automatic first down.
4. Early roughing the passer rules date back to 1938. The current rule is, according to Gear Patrol:
Roughing the passer can only be called if the quarterback is hit by a defensive player while in a “passing posture.” Additionally the defensive player has to do one of the following: lead with the crown of his helmet, make helmet-to-helmet contact, “more than mild contact”, or any contact with the head of the quarterback.
5. The head slap. According to NFL rules:
A defensive player shall not contact an opponent above the shoulders with the palm of his hands except to ward him off on the line. The exception applies only if it is not a repeated act against the same opponent during any one contact.
6. The horse collar rule goes back to 2005. This rule was recently expanded, according to Pro Football Talk:
That rule will be a bit different in the 2016 season. The league approved a proposed rule change from the Competition Committee on Tuesday that will make it illegal when a “defender grabs the jersey at the name plate or above and pulls a runner toward the ground.”
7. The chop block. The NFL defines this as
A chop block is a foul by the offense in which one offensive player blocks a defensive player in the area of the thigh or lower while another offensive player occupies that same defensive player in another form of contact
8. The passer out of the play rule:
A passer who is standing still or fading backwards after the ball has left his hand is obviously out of the play and must not be unnecessarily contacted by the defense through the end of the play or until the passer becomes a blocker, or until he becomes a runner upon taking a lateral from a teammate or picking up a loose ball, or, in the event of a change of possession on the play, until the passer assumes a distinctly defensive position
9. Below the waist tackles:
Blocks below the waist are prohibited in the following situations:
(a) By players of either team after a change of possession; or
(b) By players of the kicking team after a Free Kick, Safety Kick, Fair-Catch Kick, Punt, Field-Goal
Attempt, or Try Kick; or
(c) By players of the receiving team during a down in which there is a Free Kick, Safety Kick, Fair-Catch
Kick, Punt, Field-Goal Attempt, or Try Kick
10. Helmet as a weapon:
A player may not use a helmet (that is no longer worn by anyone) as a weapon to strike, swing at, or throw at an opponent.
11. Crackback block
At the snap, an offensive player who is aligned in a position more than two yards laterally outside an offensive tackle, or a player who is in a backfield position at the snap and then moves to a position more than two yards laterally outside a tackle, may not clip an opponent anywhere, nor may he contact an opponent below the waist if the blocker is moving toward the position where the ball was snapped from, and the contact occurs within an area five yards on either side of the line of scrimmage.