Fishback was signed as an undrafted free agent by the New York Giants after the 1990 NFL draft. He injured his back in the third preseason game and was placed on the injured reserve list, with a transverse process fracture on August 27.[5] He was released in November.
On September 4, 1991, the Atlanta Falcons signed him to their practice squad.[6] He was promoted to the active roster on November 16.[7] He played in 14 games as a reserve defensive back, posting 5 defensive tackles, 24 special teams tackles (led the team), partially blocked a punt, returned a fumble for a touchdown and returned 3 kickoffs for 29 yards. He was named the Falcons "Special Teams Player of the Week" 6 times. He was selected as a Pro Bowl alternate at the end of the season.
In the NFC Wild Card playoff game against the New Orleans Saints, with the score 27-20 and less than 2 minutes left in the fourth quarter, the Falcons cornerback Tim McKyer intercepted a pass that sealed the victory, but instead of falling down, he chose to make a risky lateral pass to teammate Deion Sanders, who after a sizeable run, made another dangerous lateral pass to Fishback, who returned the ball for an apparent touchdown, that would be overruled when proven that Sanders had done an illegal forward lateral, thus the play ended as a footnote.[8]
On March 13, 1992, he signed in Plan B free agency with the New York Jets.[9] He appeared in the first five games, collecting 4 special teams tackles. He was cut on October 20.[10]
On November 3, 1992, he signed as a free agent with the Atlanta Falcons. He appeared in the final 7 games, making 7 defensive tackles and 8 special teams tackles. On August 23, 1993, he was placed on the injured reserve list with a sprained neck.[11] He was released on October 4.
On October 13, 1993, he signed as a free agent with the Dallas Cowboys.[12] He played mainly on special teams and registered 12 special teams tackles (tied for sixth on the team).[13] He suffered a sprained right knee in the tenth game against the Phoenix Cardinals and was declared inactive for the next 5 contests. He was a part of the Super Bowl XXVIII Championship team. In 1994, he registered 17 special teams tackles (sixth on the team). He was released on November 30.[14]
In 1995, he was signed as a free agent by the Denver Broncos. He was released on August 22.[15]