14. Deron Williams
Deron Williams had the chance to be one of the best point guards in the NBA, but injuries caused his game to decline tremendously during his time with the Brooklyn Nets, and the Mavs ended up signing him to a two-year deal back in 2015.
Williams wasn't a bad player by any means for the Mavericks, but his performance was much worse than what we saw during his prime with the Utah Jazz and one year with the New Jersey Nets (before they rebranded to the Brooklyn Nets). He averaged 21.0 points during the 2011-12 season, and within two years after that, his point per game average fell to 14.3.
Dallas signed him after he averaged 13.0 points per game for the Nets while shooting 38.7 percent from the field. Williams was nowhere close to the caliber of player he was when Dallas pursued him in free agency the first few times, and the Mavs ended up waiving him during his second year with the squad.
Williams battled injuries during his time in Dallas, and it was clear that his career was nearing the end soon. After finishing the 2016-17 season with the Cleveland Cavaliers, Williams retired.
Williams was so special to watch during his prime with the Jazz, and he and Dallas happened to finally unite when it was a little too late.