Gale Sayers scored six TDs vs. the San Francisco 49ers on December 12, 1965. In this photo, Sayers eludes a group of 49ers defenders on his way to an 80-yard TD in the first quarter. (Pro Football Hall of Fame via AP Images)

Sayers avoids the tackle of 49ers linebacker Matt Hazeltine (55) to score his first touchdown of the day - an 80 yard run.

Sayers cuts upfield to score his first touchdown on a 80 yard run.

Sayers cuts upfield to score his first touchdown on a 80 yard run.

Sayers (40) dives into the end zone for his second touchdown.

Sayers finds the end zone on a 7-yard run for his third touchdown of the game.

Quarterback Rudy Bukich (10), targets Gale Sayers on a screen pass.

Sayers runs upfield after catching a screen pass from QB Rudy Bukich.

Sayers runs upfield after catching a screen pass from QB Rudy Bukich.

Covered in mud, Sayers heads upfield to score his fourth touchdown of the day on a 50 yard run.

Sayers dives into the end zone on a 1-yard run for his fifth touchdown of the afternoon.

Gale Sayers, Chicago Bears' sensational halfback, smiles happily after scoring six touchdowns against San Francisco 49ers. The Bears won, 61-20, in Chicago, Dec. 12, 1965. The remarkable Kansas rookie boosted his season touchdown total to 21, a new NFL record at the time.