Here are some more details on Sean Williams. It sounds like the former BC star has cleaned up his act and the Celtics are just trying to give him a look and an opportunity.

Source: Celtics to sign BC's Williams, waive O'Neal - Boston.com

Williams has had disciplinary issues since being dismissed from BC, including a 2009 arrest at a Denver mall while with the Nets. The Celtics did considerable background work and believe Williams will be a positive presence in the locker room.

Celtics leave trio back, to ink Sean Williams - BostonHerald.com

Williams was waived last week by the Dallas Mavericks. A talented shot blocker and defender, he can play center and power forward, substantial needs for the Celtics, who currently have Kevin Garnett, Greg Stiemsma and little else to defend the rim. "This is insurance," the source said. "He may end up not playing."

It seems that the Mavericks just had too many bigs and wanted to get more wing help. Sounds like a nice problem to have but looking at the standings, I wouldn't trade places with them right now (you know, except for the whole defending champs thing).