Williams is a tiny little back (5-8, 195) who despite his size does fit the versatile type player Chip Kelly likes. He's been a standout return man, an effective RB and a major threat in the passing game. He was even lined up as a receiver when the team would go five wide.
He led the FBS in kick return average for first year players in 2009 and improved on those numbers in 2010. He spent most of his career stuck behind two NFL bound backs in Robert Turbin & Michael Smith. When he did finally get the starting job last season, he rushed for 1,512 yards on 218 carries and 15 TDs (6.9 ypc BTW). He also caught 45 passes for almost 700 yards and 5 TDs.
He ran the 3rd fastest 40 time among RBs at the combine this year with 4.45.
He would certainly be a later round pick if drafted at all and likely isn't ever going to be a lead back in the NFL. But if he can be a threat in the return game, line up in the slot sometimes, be in on some option plays... he could be a useful player. And if Chip Kelly does install an up tempo, run heavy offense he'll need a couple of backs to rotate in and out.