In sprints, he set a personal record time of 6.69 seconds in the 55-meter dash at the 2009 LSU High School Indoor Classic.

[4] Reid enrolled at Louisiana State University, where he played for coach Les Miles's LSU Tigers football team from 2010 to 2012.

Coming out of LSU, Reid was projected to be a first- or second-round pick by a majority of NFL draft experts and scouts.

Reid competed with veterans Craig Dahl and C. J. Spillman throughout training camp, in an effort to win the job as the starting free safety.

On December 14, 2015, he recorded three combined tackles, defended a pass and had a 73-yard return after intercepting Russell Wilson in a 17–7 loss at the Seattle Seahawks.

He decided to sit out the following week as a precaution and stated that an additional factor in his decision was that the 49ers had missed the playoffs after finishing with an 8–8 record.

Reid finished the 2014 season with an impressive total of 42 combined tackles (34 solo), seven pass deflections and three interceptions in 15 starts.

On June 9, 2015, it was reported by the San Francisco Chronicle that Reid had contemplated retirement due to concerns over concussions after having suffered three in just the first two seasons of his professional career.

The following week, he made four solo tackles and had his first career sack on Cincinnati Bengals' quarterback Andy Dalton, as the 49ers suffered a 24–14 loss.

[25] With Jimmie Ward moving to cornerback, Reid became the de facto free safety entering the regular season.

With Tartt now the starting strong safety, Reid was moved to a hybrid safety/linebacker role after linebacker Navorro Bowman was granted a release and Malcolm Smith suffered a season-ending pectoral injury.

[17] On September 27, 2018, after placing starting safety Da'Norris Searcy on injured reserve, the Carolina Panthers signed Reid to a one-year deal.

Reid refused to disclose more details about the circumstances leading to his signing in a press conference later that day, citing the fact that the information pertained to his collusion lawsuit.

[36] In Week 9 against the Tennessee Titans, Reid recorded a team-high 11 tackles, sacked Ryan Tannehill once, and forced a fumble on running back Dion Lewis that was recovered by teammate Donte Jackson in the 30–20 win.

[39] Mid-way through the 2020 season, Reid was offered an opportunity to reunite with coach Ron Rivera on the Washington Football Team practice squad.

"[40] [41] In May 2018, Reid filed an official grievance letter with the NFL alleging that team owners and the league, influenced by President Donald Trump, colluded to prevent his employment due to his protest activities.

Reid was the second NFL player after Colin Kaepernick to participate in U.S. national anthem protests intended to highlight social awareness and racial injustice towards black people.

During a job interview with Cincinnati Bengals owner Mike Brown, Reid reportedly refused to say whether he would obey a rule against kneeling during the anthem.

[42][43][44][45] In Reid's introductory press conference with the Panthers on September 27, 2018, he wore a shirt that supported Kaepernick and stated that his collusion lawsuit would still proceed unimpeded.

Tepper also had been quite outspoken with his remarks about President Trump in the recent past and was more open to players expressing themselves and protesting than the rest of the team owners.

[47] When asked by reporters during the press conference about plans to protest now that he had signed with a new team, Reid did not answer the questions and cited the fact that the information pertained to his grievance.

By the Panthers' Week 15 loss to the New Orleans Saints, Reid claimed he had been drug-tested seven times during the 2018 season, even though he had played in only 11 games; accounting for a mandatory test, the probability of such an instance happening randomly is approximately 0.17%.

[49] A joint investigation by the NFL and National Football League Players Association concluded that Reid's claims about the number of times he was drug-tested were inaccurate.

[51] Since Reid decided to protest with Colin Kaepernick in the 2016 NFL season, the two have been collaborating to address social justice issues and help communities and people in need.