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Ricky Williams, when drafted by the New Orleans Saints in 1999, was considered to be one of the best running backs to ever come out of college football.
Williams had a lot of success with the Saints from 1999-2001. During the 2000 season, he ran for 1,000 yards and nine touchdowns in just 10 games. In 2001, he then ran for 1,245 yards.
They moved him to the Miami Dolphins the following season, and boy did he go off. He ran for 1,853 yards with 16 touchdowns in 2002. He didn't do quite as well in 2003, but 1,372 yards and nine touchdowns is not too shabby.
After that season, things were not looking good though. Williams was dealing with depression and social anxiety disorder, and he had tested positive twice for marijuana use.
He retired before the 2004 season—with a third positive test looming—but would later return to the team in 2005. He played in 12 games after serving his four game suspension for his drug usage.
Before the 2006 season, he tested positive for the drug once again and was suspended for the entire coming season.
With a planned return to the game in 2007, it was reported that Williams had tested positive yet again. NFL commissioner Roger Goodell eventually reinstated Williams, but put him on strict drug testing policy.
He has found success with the Dolphins and Baltimore Ravens since then, but he definitely threw away the years of his prime.