Reason

• In 1905, 18 people were killed playing football at all levels and 149 were injured, according to the NCAA. President Theodore Roosevelt, a football fan, met with leaders of then-football powers Harvard, Princeton and Yale at the White House in September 1905 to discuss making football safer. The sport's leaders agreed to rule changes, which benefited players in the American Professional Football Association--later changed to the NFL--when the league started in 1920.
  
  

Rules

• The NFL rules often change with the players' safety in mind. For example, in 1956 the league ruled that players couldn't grab an opponent's face mask other than the ball carrier's face mask (which was made illegal in 1962). In the late 1970s and 1980, several rule changes made football safer like players could no longer directly club, strike or swing at an opponent's face, head or neck. Through the 21st century, the NFL tweaks its rules to keep players healthy.
  
  

Helmet

• Players wore soft leather helmets in the early 1920s, which evolved to hard leather helmets in the 1930s and 1940s. In 1943, the NFL made helmets mandatory and they switched from leather to hard plastic. Today, helmets feature an extra pad on the outside to help protect against concussions.