Brock spent his freshman and sophomore years playing safety for Mississippi Gulf Coast Community College. In his sophomore year, he and the rest of Mississippi Gulf Coast Bulldogs had an undefeated season with a 12-0 record and a spot in the National Junior College Athletic Association championship game which his team won by a margin of 62-28 over Kilgore College. That season he recorded 59 tackles, 11 interceptions and two forced fumbles. During his time there, he was teammates with Terrence Cody. In his junior year, Brock transferred to the University of Minnesota. He was made a starter and was third on the team in tackles with 73. Brock posted an interception, six passes defended, three forced fumbles, and one fumble recovery on the year. After only one season, he left the University of Minnesota after being suspended for failing to qualify academically. In 2009, Brock transferred to Belhaven University of the National Association of Intercollegiate Athletics to finish out his senior year. He posted 51 tackles, 2.5 sacks, six interceptions, 10 passes defensed and one fumble recovery as a senior at Belhaven.
Professional career
San Francisco 49ers
2010 season: Rookie year
Brock signed as an undrafted free agent by Buffalo bills after going unselected in the 2010 NFL Draft on April 26, 2010. The team later released him on September 14, 2010, but signed with the practice squad the next day. Five days later, he signed on to the active roster. Brock would be released again on October 12, then put on the practice squad two days later. He was signed to the active roster on October 27. Brock made his NFL debut against the Denver Broncos and that year only played in three games and recorded only four tackles.
2011 season
In 2011, Brock played in 11 games but he missed three games due to a hand injury. That year Brock recorded six tackles and two interceptions. He got his first interception in the first game of the season versus the Seattle Seahawks and his second versus the Dallas Cowboys with an 18-yard return.
2012 season
Brock later signed a one-year deal with the 49ers on March 12, 2012. During the 2012 season, Brock played all 16 games, mostly on special teams, and recorded 16 tackles for the year. During a game against the St. Louis Rams, he forced a key fumble late in the game that led to a go-ahead score by the 49ers. At the end of the 2012 season, Brock and the 49ers appeared in Super Bowl XLVII. He contributed on special teams, but the 49ers fell to the Baltimore Ravens by a score of 34–31.
2013 season
In the 2013 offseason, Brock signed a $1.323 million tender with the 49ers keeping him there until the 2014 season. Brock played all 16 regular-season games and opened all three postseason games with San Francisco, registering a career-best five interceptions. Brock added 35 tackles and 13 passes defensed, along with 11 tackles in three postseason games. On October 6, 2013, Brock scored his first touchdown against the Houston Texans on an interception off quarterback Matt Schaub. Later in the game, Brock recorded his second interception of the game, making it the first multi-interception game in his career. Brock was named the team's third cornerback, replacing the injured Nnamdi Asomugha, who was later released by the team. After the game against the Texans, Brock was named NFC Defensive Player of the Week. On November 22, 2013, Brock agreed to a four-year extension with the 49ers worth $16 million including $7 million in guaranteed money. When Tarell Brown went down with a rib contusion in a Week 11 loss against the New Orleans Saints, Brock took over as duties as starting cornerback. Brock was a key part of a memorable play in Week 16, on Monday Night Football against the Atlanta Falcons. The game was a rematch of the previous year's NFC Championship game and the last regular-season game at Candlestick Park. Matt Ryan had just thrown a 2-yard touchdown pass to Tony Gonzalez with 2:09 remaining to make it a 27-24 game. Atlanta recovered the subsequent onside kick and completed 2 quick passes to get down to the 49ers 10-yard line. On the next play, Brock deflected a pass by Matt Ryan, which was caught by teammate NaVorro Bowman. Bowman returned the interception 89 yards for a game-sealing touchdown. Brock finished the game with an interception in the end-zone as time expired.
2014 season
Brock's 2014 campaign was, unfortunately, a lost cause for him and the 49ers. He struggled with a toe injury throughout the majority of the season that he sustained in a Week 1 victory over the Dallas Cowboys and ended up only playing 3 games and recording 7 tackles. Without the presence of their number 1 corner, the 49ers struggled to find a consistent replacement to take over the nickel duties as they now moved Perrish Cox out of that position to fill Brock's role.
2015 season
Brock opened all 15 games with the 49ers, posting 53 tackles, three interceptions, and 11 passes defensed. Brock notched multiple passes defensed in three different games. In the season-opener, he recorded 3 tackles as well as an interception against the Minnesota Vikings. During Week 5, Brock grabbed his second interception of the season against the New York Giants. As the second quarter was about to end, Manning tried to throw a touchdown to Beckham, but Brock's tight coverage gave him the interception. During Week 8 of the 2015 Season, Brock picked off quarterback Russell Wilson during the end of the second quarter to tie cornerback Kenneth Acker with the most interceptions on his team. According to Pro Football Focus, Brock received a +3.0 coverage grade by the end of Week 13.
2016 season
In 2016, Brock started all 16 games for the first time in his career and finished the season with 59 combined tackles, 14 passes defended, an interception, and 1 forced fumble. He tallied more than five tackles in five different games throughout the season. During Week 16 against the Los Angeles Rams, Brock intercepted Jared Goff and returned it 39 yards as the 49ers narrowly won 22-21. On April 7, 2017, Brock was released by the 49ers after a domestic violence incident.
Seattle Seahawks
On August 16, 2017, after his domestic violence case was dismissed, Brock signed with the Seattle Seahawks on a one-year deal.
Minnesota Vikings
On September 1, 2017, Brock was traded to the Minnesota Vikings for a 2018 seventh-round draft pick. Brock appeared in 11 regular-season games and two playoff games with the Vikings. He recorded six tackles and one pass defensed in addition to two special-teams stops.
Denver Broncos
On March 14, 2018, Brock signed a one-year contract with the Denver Broncos. Coach Vance Joseph said Brock will compete with Bradley Roby for the No. 2 cornerback spot. He was named the third cornerback on the depth chart, playing in 12 games with five starts recording 23 tackles and six pass deflections.
On April 2, 2019, Brock signed a one-year contract with the Arizona Cardinals. He was named a starting cornerback opposite rookie Byron Murphy to begin the season in place of the suspended Patrick Peterson. He played in 10 games with seven starts before being released on December 2, 2019.
On December 3, 2019, the Tennessee Titans claimed Brock off waivers.
NFL statistics
Regular season
Postseason
Legal Issues
On April 7, 2017, Brock was arrested in Santa Clara County, California following an alleged incident which left his children's mother with visible injuries. Because of this incident, Brock was released by the 49ers. On August 9, 2017, the case against Brock was dismissed due to a lack of evidence. On January 5, 2018, the NFL formally cleared Brock from violation of the league's personal conduct policy.
