A rough competitor who puts out the kind of pursuit that upsets running backs and terrorizes quarterbacks. At Notre Dame, Fanning accounted for 164 tackles. Fanning was a starter at defensive tackle in 1973 and 1974. He was a 1974 All-America selection by the Walter Camp Foundation, The Sporting News, NEA, Time and was a Second-team All-America selection by the AP. In his years at Notre Dame he shared the practice field with Daniel "Rudy" Ruettiger whose saga was made into a Hollywood film, "Rudy."
Notre Dame ranked 2nd in the nation in total defense in 1973 and the Irish claimed the National Championship with an 11-0 record. In 1974 the defense ranked first in the nation, allowing only 195.2 yards per game and were ranked 6th in the nation in the final AP poll.
Fanning was drafted on the First round (9th selection) of the 1975 NFL Draft by the Los Angeles Rams. He was touted to be the successor of Merlin Olsen who was entering his 14th season in 1975. In 1976, in spot duty for Olsen, Fanning recorded 4 sacks.
Fanning took over as the starter at left tackle in 1979 after an injury to Cody Jones. Fanning had 8 sacks in 1979 and 10 sacks in 1980. He led the Rams in sacks in the strike-shortened 1982 season with 5.
Prior to the 1983 season Fanning was traded to the Detroit Lions. He played one season with the Lions and was signed as a free agent by the Seattle Seahawks in 1984. He had 7 sacks in 1984 as a pass-rush specialist for the Seahawks.