Hoaglin graduated from East Palestine High School in East Palestine, Ohio and University of Pittsburgh, from where he was eventually drafted by the Cleveland Browns in the 1966 NFL draft.
He was a member of the first Seattle Seahawks team after being acquired from the Houston Oilers in the 1976 NFL Expansion Draft.
After he retired as a player, Hoaglin served as an assistant coach for the Detroit Lions (1978–1984), New York Giants (1985–1992), New England Patriots (1993–1996), and Jacksonville Jaguars (1997–2000), serving under the Bill Parcells coaching tree during his stints at the last three franchises.
He was an assistant coach for the Giants during their Super Bowl XXI and Super Bowl XXV championship seasons under Parcells, then won an AFC Championship at New England under Parcells in 1996 before the Patriots fell 35–21 to the Green Bay Packers in Super Bowl XXXI.
This biographical article relating to an American football offensive lineman born in the 1940s is a stub.