As first reported by ESPN's Adam Schefter, the Titans have met with former Saints defensive coordinator Gregg Williams about becoming an assistant head coach. Williams is currently under suspension by the NFL for his role in the Saints' Bountygate scandal, but has received permission to talk to teams about a new job. Jim Wyatt indicates that if Williams is brought on, Jerry Gray is expected to remain the defensive coordinator. Gray and Williams have worked together in the past, including in Williams' past stint as defensive coordinator with the Titans, in Buffalo, and in Washington.
Williams' hire is likely to be a controversial one for several reasons. First, his role in the Bountygate scandal, when under questioning by NFL officials he went ahead and named names of players who had a role. Regardless of your feelings about that, NFL players may understandably feel constrained in their dealings with him. Williams will have to deal with the issue forthrightly to establish a bond with his players. Fortunately (or not), the Titans do not seem to have a strong leadership core in place that Williams will have to work with and through in selling his message to the team in whatever position he ends in.
Second, Jeff Fisher reportedly attempted to hire Williams for another stint in Tennessee after Jim Schwartz left to become head coach of the Lions. One of Williams' conditions of hiring it seems, though, was that the team hire his son Blake as an assistant. This apparently run afoul of Bud Adams' anti-nepotism rule, and when the Saints would indeed hire Blake Williams along with Gregg, father and son went there. Fisher did hire Blake as his linebackers coach in St. Louis, but he was fired after the 2012 season for his arrogance and failure to get along with players. As I noted recently, the Titans seem to have a full complement of coaches, and there doesn't seem to be a job for Blake, at least right now.
Third and most importantly, Williams has in recent years coordinator mostly not very good defenses.