At the University of California, Los Angeles, Davis played defensive end. He redshirted his freshman year in 2003. In 2004, he played in all 12 games, starting the first two contests, at defensive end. He had 17 tackles and 2.5 sacks. In 2005 Davis moved to outside linebacker from defensive end during the spring and played both positions early in the season before moving back to end due to injuries on the team. He appeared in all 12 games and his 28 tackles for the season and was tied for third on the team with two sacks and was sixth with six tackles for losses. As a junior in 2006, he was named first-team All-American by CollegeFootballNews.com and SI.com and he was selected second team All-Pacific-10 Conference. On the year, Davis made 47 tackles, with 12.5 sacks and 17.5 tackles for loss. In 2007, he was a Second-team All-American choice by The NFL Draft Report and the Walter Camp Foundation and was first-team All-Pac-10 Conference. He was a semifinalist for the Bednarik Award and was on the watch lists for the Lott, Nagurski, Lombardi and Hendriks Awards. He started all 13 games at right defensive end, ranking tied for ninth in the nation and tied for first in the league with 12 sacks. He ranked sixth in the Pac-10 with 15.5 stops for losses. On the year he recorded 45 tackles caused two fumbles and recovered another and deflected nine passes and defensed 3 others. Davis ranks second in school history with 29 quarterback sacks, topped only by Dave Ball’s 30.5. His 42.5 stops for losses rank third in school annals behind Ball and Carnell Lake.
Professional career
Pre-draft
Pittsburgh Steelers
Davis was drafted by the Pittsburgh Steelers in the third round of the 2008 NFL Draft. After being drafted by the Steelers, he was converted to outside linebacker in the Steelers' 3-4 defense, though faced difficulty in the transition, as he was inactive for most of his rookie season. He was waived on September 4, 2009.
Davis was signed to the New England Patriots practice squad on October 7, 2009. After spending the remainder of the season on the practice squad, he was re-signed to a future contract on January 13, 2010. The Patriots waived Davis on May 27, 2010.
Davis was signed by the San Francisco 49ers on August 10, 2010. On September 3, 2010, Davis was cut from the 53-player roster that would go on to play regular season games. The 49ers then re-signed him to their practice squad on September 5, 2010; he was released from his contract nine days later. He was re-signed to the practice squad on September 22.
Oakland Raiders
On October 5, 2010, the Oakland Raiders signed Davis to their active roster to help bolster the team's injury-depleted linebacker corps. He was waived a year later on October 13, 2011.
On November 23, 2011 the Cincinnati Bengals signed Davis to their practice squad.
Second Stint With the 49ers
On January 3, 2012, the San Francisco 49ers signed Davis to their practice squad.
Hamilton Tiger-Cats
On August 4, 2012, Davis was signed by the Hamilton Tiger-Cats and assigned to their practice squad. On August 16, he was promoted to the active roster and started his first career game vs. Winnipeg.
