Coach Mike Nolan also dismissed defensive line coach Gary Emanuel in a shakeup to fix a defense that was largely the responsibility of Nolan, a longtime defensive coordinator for four NFL teams.

Davis joined Nolan's staff in 2005 after one season as New York Giants linebackers coach and three previous seasons in the same position with Atlanta. With little talent or depth in San Francisco, his first defense allowed 428 points last season — third worst in the NFL — and finished dead last in several statistical categories.

Though Nolan was heavily involved in defensive game-planning, Davis took much of the public heat as the 49ers' defense had several terrible games this season, most notably giving up 41 points by halftime in a blowout loss to the Chicago Bears. The unit improved markedly in the second half of the season, yet still finished with unimpressive statistics.

Nolan refused to give a vote of confidence to Davis when he wrapped up the season Tuesday, saying only, "I think Billy did a good job."