Amazing player who retired much too early.

Brown told Maule: “I could have played longer. I wanted to play this year, but it was impossible. We’re running behind schedule shooting here, for one thing. I want more mental stimulation than I would have playing football. I want to have a hand in the struggle that is taking place in our country, and I have the opportunity to do that now. I might not a year from now.”

And later this: “I quit with regret but not sorrow.”

In summer training camps around the league that year, players were stunned. “I heard it and I didn’t believe it,” says Dick LeBeau, at the time a Pro Bowl defensive back with the Lions. “He was much too good and much too young to retire. But I will also say that we weren’t sorry to see him go.” Ed Khayat, then 31, had come into the league with Jim Brown in 1957 and played against him 18 times in nine seasons with the Eagles and Redskins. He heard about the retirement while working out for one last season with the Boston Patriots of the AFL. “I thought it was impossible that Jim Brown was going to retire,” said Khayat. “His play hadn’t dropped off at all. I just couldn’t imagine it.”

Adrian Peterson would have to average 1,900 yards per season for the next three full seasons to match Brown’s per-game rushing mark, the 56-game hitting streak of NFL records.

For goodness sakes, don't forget his movie career!http://www.imdb.com/name/nm0000987/

Right, he was filming the Dirty Dozen when he decided to quit football. 

Apparently movies offer more mental stimulation than football.