Hallen was a four-year starter playing college football for the Kent State Golden Flashes, starting 44 consecutive games.
He was a first-team All-Mid-American Conference choice in 1997 after switching to right tackle after three seasons at center.
Hallen was selected in the 1998 NFL draft by the Atlanta Falcons in the second round [2][3] (53rd overall) and went on to play in Super Bowl XXXIII.
Hallen's career came to an end on August 11, 2006, when he announced his retirement due to ongoing problems with his back, which he first injured in the 2001 season while playing for the Falcons.
Hallen announced his retirement shortly after he was named the Browns' starting center in place of injured LeCharles Bentley.