Barr was an offensive player his first two years at UCLA, playing running back, wide receiver, and tight end.

He struggled as a running back, and switched to linebacker during his junior year, at which position he was named a first-team All-Pac-12 selection and to the CBSSports.com All-America second-team.

Barr was born in South Bend, Indiana, but raised in Los Angeles, where he attended Loyola High School in the Pico-Union neighborhood.

[1] However, he missed virtually all of his senior season after breaking his ankle in the September, and was also unable to participate in the 2010 U.S. Army All-American Bowl, to which he was invited.

With scholarship offers from dozens of schools, Barr narrowed his decision down to Notre Dame and UCLA, before choosing the Bruins on January 21, 2010.

[6] Barr was an offensive player his first two years at the University of California, Los Angeles, playing running back, wide receiver and tight end.

[15] In a November 2012 game against the USC Trojans, Barr sacked quarterback Matt Barkley, who suffered a season-ending shoulder injury.

For the 2013 regular season, Barr had 62 tackles, 20 for a loss (ranked 9th) and has forced five fumbles (fifth best) and recovered four (second in the nation).

On December 11, 2013, Barr was named a first-team All-American by the USA Today,[26] becoming the first UCLA player since Kai Forbath to do so.

[29] At the 2014 NFL Combine, Barr ran the 40-yard dash in 4.66 seconds, sixth-best among linebackers, and tied for 14th in the vertical (34.5 inches).

At the UCLA Pro Day on March 11, he ran an electronic 4.41 in the 40-yard dash, did 19 repetitions on the bench press and had a 10-foot-5 (3.20 meters) broad jump.

He was a top contender for defensive rookie of the year and one of three Viking defenders named to the Pro Football Focus All-NFC North Team.

[39] In the first game of the season, Barr played all 73 defensive snaps against the San Francisco 49ers and recorded a career-high 12 tackles.

[40] In a Week 4 loss against the eventual Super Bowl 50 champions Denver Broncos, Barr recorded his first career interception off a pass thrown by Peyton Manning.

[47] On October 15, 2017, during the Vikings 23–10 victory against the Green Bay Packers, Barr recorded a hit that knocked Aaron Rodgers out of the game, injuring his collarbone.

[48] In an interview with Conan O'Brien, Rodgers claimed that Barr gave him "the finger" and told him to "suck it".

[52] On December 22, 2019, the Minneapolis Star Tribune received criticism from Packers fans after the newspaper included a photograph of Barr's hit on Rodgers in a column as one of the best Minnesota sports moments of the decade.

[53] In the Vikings' Divisional Round win over the New Orleans Saints, Barr intercepted a Drew Brees pass that was tipped at the line of scrimmage by teammate Everson Griffen.

[54] On October 21, 2018, Barr suffered a hamstring injury against the New York Jets, ending a streak where he started in 44 games.

[60] On October 26, 2019, Barr received a fine for a hit on Matthew Stafford during a Week 7 matchup against the Detroit Lions.

In the divisional round of the playoffs against the 49ers, Barr forced a fumble on running back Matt Breida and recovered the football, but the Vikings lost 27–10.

In March, the team reworked his contract and Barr was allowed to become a free agent at the end of the season.

[8] On June 27, 2018, it launched new emergency grant funding at Loyola High School, raising $50,000 in assistance, ticket sales, and auctioning.