The evolution of the NFL has been stark over it’s illustrious history. In those early years of the 1920’s and 30’s players had different responsibilities then they do today. The quarterback was still the signal-caller, but his job was to basically hand off the ball and block. It was the halfbacks and fullbacks that did everything.
That’s right, the halfbacks and fullbacks were expected to run, block catch and, yes, they were the passers too. In that time period whoever heard of a quarterback throwing the ball? That was just crazy talk.
As time marched on into the 1950’s and 60’s, the halfbacks and fullbacks had become pure runners that were also asked to block.