Bailey started for his second year at strong-side linebacker as a sophomore in 2012 and had another impressive season. Overall in 2012 while starting all 13 games, he had 80 tackles (third on team), including 8 for losses (with 1 sack), plus 5 deflections, a forced fumble and a team-best 4 interceptions. His 4 interceptions were tied for second most by a linebacker in the nation in 2012. He made 2012 CollegeFootballNews.com Sophomore All-American honorable mention and All-Pac-12 honorable mention. He had a team best 7 tackles (1 for a loss) against Hawaii, 8 tackles (1 for a loss) and 2 interceptions against Syracuse, 9 stops (1 for a loss), a deflection and an interception at Stanford and 8 stops against California. He had 3 tackles and a deflection at Utah, 7 tackles, an interception to set up a TD and forced a fumble at Washington and a tackle against Colorado. He had 9 tackles (2 for losses) at Arizona, 10 tackles (including 2 for losses, with a sack) against Oregon and a tackle against Arizona State. He had 8 tackles (1 for a loss) at UCLA, 4 tackles and 2 deflections against Notre Dame and 5 tackles against Georgia Tech.
Bailey, who was moved from safety to linebacker prior to 2011 spring practice, earned the starting job on the strongside as a redshirt freshman in 2011 and had a stellar showing all season. Overall in 2011 while starting 11 games (all but Colorado), he tied for the team lead in tackles with 81, including 2 sacks, plus he had 2 deflections, 2 interceptions and a forced fumble. He and fellow linebacker Hayes Pullard were the first freshmen to lead USC in tackles since records were first kept in 1954. He suffered a concussion against Stanford and missed the Colorado game. He was named the 2011 Pac-12 Freshman Defensive Player of the Year and made the All-Pac-12 second team. He was the Defensive Freshman of the Year on the 2011 CollegeFootballNews.com Freshman All-American first team and made the 2011 Football Writers, Sporting News, CBSSports.com, YahooSports.com, FoxSportsNext.com and Phil Steele Freshman All-American first team. He made 2011 SI.com All-American honorable mention. He made the 2011 Phil Steele All-Pac-12 second team. He had 7 tackles against Utah, then a team-best 9 tackles (with a sack) and a fumble recovery against Syracuse, a game-high 10 tackles (with a sack) and added a deflection at Arizona State, a game-high and career-best 14 tackles (the most by a USC freshman since Chris Claiborne's 20 in 1996 against Arizona State) and 1 deflection against Arizona and a team-best 8 tackles and 2 interceptions (the first in the end zone at the end of the first half to keep Cal scoreless as it was driving and the second late in the game to set up a USC TD) at California to earn College Football Performance Awards National Linebacker of the Week honors. He added 6 stops at Notre Dame, then a game-high 13 tackles against Stanford before suffering a concussion. After missing the Colorado game, he had 2 tackles against Washington, 7 tackles at Oregon and 5 tackles against UCLA.
Bailey redshirted as a freshman safety in 2010, his first year at USC.
His 2009 honors included Prep Star All-American, Prep Star Dream Team, Super Prep All-Farwest, Prep Star All-West, Orange County Register Fab 15 second team, Long Beach Press-Telegram Best in the West Best of the Rest, Tacoma News Tribune Western 100, Cal-Hi Sports All-State second team, All-CIF Pac-5 Division first team and All-Moore League first team as a senior defensive back at Lakewood (Calif.) High. He had 70 tackles, 8 deflections, 3 interceptions and 1 fumble recovery in 2009. As a junior in 2008, he made Cal-Hi Sports All-State Underclass first team and All-Moore League. He had 72 tackles, 11 deflections, 9 interceptions and 2 forced fumbles in 2008.
He is a policy, planning and development major at USC. He and 15 of his USC teammates spent 5 days in Haiti in the spring of 2012 building homes and assisting those in need.