10. Gilbert Arenas
The Golden State Warriors had done everything right. Their scouting team had identified Arizona point guard Gilbert Arenas as a sleeper in the 2001 NBA Draft, taking him with the second pick of the second round. Arenas developed quickly, averaging 18.3 points and 6.3 assists per game by his second season and winning Most Improved Player.
After that year, however, Arenas became a restricted free agent. The Warriors were over the salary cap but offered him the largest contract that they legally could. Rather than commit to stay with the team that had drafted him and developed him, Arenas allegedly "flipped a coin" between the Warriors and the two other teams interested in him, the Washington Wizards and Los Angeles Clippers (the jury is still out on what kind of three-sided coin he used).
When Arenas chose the Wizards, they signed him to a six-year, $60 million contract. If Arenas was a first-round pick, the Warriors would have been able to use an exception to go "over the cap" and match the offer. As a second-round pick, the Warriors were unable to match the offer, and he left for the Wizards and would make three-straight All-NBA teams over the next three seasons.
The Warriors' heartbreak would lead to a new provision being written into the league's Collective Bargaining Agreement, dubbed the "Arenas Rule" after the breakup. Teams over the cap would now be allowed to re-sign their second-round restricted free agents up to a certain amount. It was too late to stop Arenas from deserting the Warriors in 2003.