He became the starter at quarterback in the seventh game of his sophomore season in 1988, after passing Daniel Ford on the depth chart.
He also spent two days in a hospital with a probable case of appendicitis, that was later diagnosed as a gastrointestinal problem and caused him to lose 17 pounds.
In 1997, he started 4 games, while Harbaugh recovered from a fractured right hand he suffered when he scuffled with NBC sportscaster Jim Kelly.
Coming in with an 0–10 record against the defending Super Bowl champions Green Bay Packers, he led the team to a 41–38 win, completing 24-of-30 attempts for 340 passing yards.
The Cincinnati Bengals acquired Justin after the retirement of Boomer Esiason to compete with Jeff Blake for the starting job.
[10] The St. Louis Rams acquired Justin to provide depth at quarterback, after Trent Green suffered a serious left knee injury in the last preseason game and Kurt Warner was named the new starter.
On March 30, 2000, he was signed as a free agent by the Dallas Cowboys, to replace the departed Jason Garrett as the backup quarterback.
[11] After struggling in preseason (he accounted for 6 critical turnovers in the first two games) and the signing of Randall Cunningham, he was waived injured on August 24.