From wiki -- flushed career with holdout

During his rookie season, he rushed for 1,151 yards and seven touchdowns for the Broncos as they qualified for Super Bowl XXIV, but were defeated 55-10 by the San Francisco 49ers. Humphrey, although finishing the game as the Broncos leader in both rushing (61 yards) and receiving (31 yards), had a key turnover in the first quarter when he fumbled near midfield. Following this fumble, the 49ers would score 34 unanswered points to put the game away. Humphrey was not named NFL Rookie of the Year, due to Barry Sanders' incredible 1,470-yard rookie campaign. He followed his impressive rookie performance with a Pro Bowl selection in 1990, rushing for 1,202 yards and seven touchdowns in 1990. Humphrey was the first Denver Bronco to rush for 1,000 yards in back-to-back seasons.

In 1991, Humphrey held out of training camp in hopes of obtaining a new contract. The Broncos, by team policy, refused to renegotiate his pay and the holdout continued late into the season.

Unable to secure a new contract, Humphrey finally ended his holdout in week 14. However, by that time, newly signed Gaston Green had emerged as the team's starting running back and was on his way to completing his own 1,000-yard season. Furthermore, Humphrey had fallen out of favor with the team's coaching and front office as a result of the holdout. When Humphrey returned in week 14, he was out of shape and given only a reserve role in the Broncos' offense. He remained on the bench as Denver made a run to the AFC Championship Game, losing to the Buffalo Bills 10-7.

The following offseason he was traded to the Miami Dolphins in exchange for running back Sammie Smith. He played for the Dolphins in 1992 scoring only one touchdown and running for 471 yards. Ironically, Humphrey's team made it to the AFC Championship Game in 1992, only to lose again to the Buffalo Bills. He finished his NFL career with the Buffalo Bills in 1995.