When did the NFL impliment the rule that a player can continue to run if not down by contact?

I'm looking for the year when this rule was put into play.

When did the NFL impliment the rule that a player can continue to run if not down by contact?nba gear

It's always been the rule. Up until about 40 years ago, he actually had to be tackled; if he was knocked down by a contact but not actually tackled, he could get up and continue to run.

When did the NFL impliment the rule that a player can continue to run if not down by contact?nba finals 2007 ,nba teams

Not positive, but I think that was a AFL rule the the NFL implimented when they merged. Some time around 1974?