Blair was an All-American selected out of Iowa State University by the Vikings in the second round of the 1974 NFL Draft with the 51st overall selection. Blair quickly established himself as one of the top and speediest linebackers in the NFC, earning Pro Bowl honors for 6 consecutive seasons (1977–1982) and making the NFL All-Rookie Team. In addition, Blair was selected All-Pro in 1980, All-NFC in 1978 & 2nd Team All-NFC in 1977, 1979 & 1981. He was also an exceptional special teams player, particularly in blocking punts because of his great speed and timing abilities. Blair is 3rd in the NFL with 20 blocked kicks.
Blair started for the Vikings his rookie season for the injured Roy Winston. Blair participated in special teams play in Super Bowl IX, blocking Bobby Walden's punt, recovered by Terry Brown (American football) in the endzone, the Vikings' only points all day, as they missed the extra point. He was a vital part of the Vikings' 1976 season of 11 wins, 2 losses, and 1 tie, second in the NFL in least points allowed (176 points, 12.6 points per game). In particular, Blair recovered 5 fumbles and intercepted 2 passes from his linebacker position with Jeff Siemon in the middle and Wally Hilgenberg on the opposite side. The Vikings defeated the Rams again in the NFC championship game of the 1976-77 NFL playoffs, when Blair recovered 2 fumbles.