Michigan Wolverines Football History and Traditions
Michigan Football Retired Jerseys - University of Michigan Athletics
U-M's Retired Jerseys - University of Michigan Athletics
UM's Howard on jersey retirement: 'I wanted to make 21 significant'
Nigeria-born, Scotland-raised, Michigan football LB continues remarkable rise - mlive.com
Michigan Football on Twitter: "Ron Kramer's No. 87 will be one of six jersey numbers to be officially retired on Saturday. #GoBlue https://t.co/aPsLx7opPM"
Da Greats: Retired Chicago Bears Jersey Numbers - The Chicago Audible
Michigan football junior Devin Gardner officially switches to No. 12, still listed as a QB