Armstrong attended Farragut High School in Chicago, and was inducted into the Chicagoland Sports Hall of Fame.
Before his NFL career, Armstrong played for Purdue University, becoming the school's all-time leading rusher and leader in all-purpose yards.
[2] He still holds the Purdue single game rushing record (276 yds vs. arch-rival Indiana.)
[3] Armstrong became the 13th Boilermaker (nine players, four coaches) inducted into the College Football Hall of Fame.
In the 1977 season, he assisted the Denver Broncos to an appearance in Super Bowl XII, which they lost to the Dallas Cowboys 27–10.