Marshall recovered an NFL record 29 opponents' fumbles, including his 1964 "wrong-way run", a play in which he recovered a fumble and returned it 66 yards in the wrong direction into his own end zone, where he threw the ball out of bounds, resulting in a safety for the San Francisco 49ers.

He was also a track star at Ohio State, setting school records at discus and shot put in 1958.

[7][8] Along with Marshall, the team included other future NFL players like Jim Houston, Dick LeBeau, and Bill Jobko.

[6] Marshall left school before his senior year, primarily for financial reasons, and played for the Saskatchewan Roughriders of the Canadian Football League (CFL) in 1959.

After one year, he was traded to the Cleveland Browns in an NFL–CFL transaction, being swapped for Bob Ptacek, who had played against Marshall in college at the University of Michigan.

[14] Cleveland's Paul Brown had selected Marshall in the fourth round of the 1960 NFL draft, obtaining the rights to sign him.

He contracted encephalitis during military training before the 1961 season, and was seriously ill, even being placed in an induced coma to save his life.

[18] Marshall started 270 consecutive games while playing for the Vikings, an NFL record since surpassed by Brett Favre.

[14] He was a member of the Vikings' famous "Purple People Eaters" (which consisted of Marshall (DE), Alan Page (DT), Gary Larsen (DT), and Carl Eller (DE)),[20][21] and was the final player from Minnesota's initial expansion team of 1961 to retire.

After recovering an offensive fumble, Marshall ran 66 yards the wrong way into his team's own end zone.

"[31] Despite the gaffe, the Vikings won the game 27–22, thanks to a forced fumble by Marshall, which Eller returned for a touchdown.

Marshall later received a letter from Roy Riegels, infamous for a wrong-way run in the 1929 Rose Bowl, stating, "Welcome to the club.