He was also an Arena Football League (AFL) player, who played quarterback for the Albany Firebirds and the Fort Worth Cavalry.
As a student (at Spring Hill High School in Longview, Texas) he set multiple passing records and was selected to the all-state team in both his Junior and Senior years.
As a Freshman in 1980, he backed up All-American and future All-Pro Wade Wilson, a year in which the Lions were NAIA National Semifinalists.
As a Junior Mackey threw for 1,667 yards and 11 touchdowns and led the Lions to a 6–4 record, good enough for LSC conference runner-up (2nd place).
As a Senior in 1983 Mackey led the Lions to a share of the Lone Star Conference Championship with an 8–2 record, throwing for 1,960 yards and 14 touchdowns and was named the LSC Second-team All-Conference team.