Williams busted out of the league after being selected with the No. 11 overall pick in 2009. The 6'6 Williams seemed promising in his first year, starting nine games for a mediocre New Jersey Nets squad. His shooting touch was lacking, but he had the athletic abilities to make it in the NBA as a rangy shooting guard or small forward. However, during his sophomore season he was traded to the Houston Rockets in a deal that brought Sasha Vujacic to the Nets. He never fit in there, appearing in just 23 games over two years before getting waived, after which he had a brief stint with the Sacramento Kings last season. He was waived by the Detroit Pistons after training camp, then spent the beginning of this year in China before coming back to the United States due to a death in the family.
The Celtics have been hurt on the injury front. The problems started in late January, when they lost one of the NBA's elite point guards in Rajon Rondo, out for the season with an ACL injury. Next, in early February, rookie big man Jared Sullinger had a promising debut season ended by back surgery. Then, shortly before the All-Star break, one of Rondo's backups, Leandro Barbosa, suffered the same injury as Rondo, ending his year as well. That left the team with 10 healthy players before the Williams signing.
With those injury woes in mind, it's a little bit strange that they chose to go with Williams rather than someone who slots in at point guard or a power forward. As of right now, Avery Bradley, Courtney Lee, and Jason Terry are the entire guard rotation, with Terry -- who has developed into a bench shooter in the latter half of his career -- the most point guard-like of the three, leading healthy guards with 2.4 assists per game. Williams can provide depth as a shooting guard, but he has no point credentials.