[2] Though he had played defensive end since high school, Alexander switched to linebacker when he transferred to Utah State University.
The teammate, running back Joseph DeMartino, was knocked unconscious and required surgery for injuries to the face and eye.
Facing a year in jail, he entered a guilty plea to reduced charges, receiving a one-year sentence with all but 45 days of it suspended.
[11] Defensive coordinator Gregg Williams was cited as one of the top contributing factors in the selection of Alexander and claimed he would take awhile to develop, but would be comparable to Sean Taylor after doing so.
[13][14] Throughout training camp, Alexander competed for a job as a backup safety against Cody Davis, Christian Bryant, Lamarcus Joyner, and Matt Daniels.
[16] He made his professional regular season debut in the Rams' Week 2 matchup at the Tampa Bay Buccaneers, but only appeared on special teams during their 19–17 victory.
[19] During training camp, Alexander competed against Mark Barron and Davis to be the Rams' primary backup strong safety.
[24] On December 9, 2015, the Rams placed McDonald on injured reserve for the remainder of the season due to a shoulder injury and named Alexander his replacement at strong safety for the last four games.
[26] He finished the 2015 season with 39 combined tackles (30 solo), two sacks, a pass deflection, and a fumble recovery in 14 games and five starts.
[29] On December 11, 2016, Alexander recorded four combined tackles before exiting the Rams' 42–14 loss to the Atlanta Falcons in Week 14 due to a possible concussion.
[32] The following day, Los Angeles Rams' general manager Les Snead fired Fisher and named special teams coordinator John Fassel the interim head coach for the last three games of the regular season.
[33] Alexander finished his first season as a full-time starter with a career-high 50 combined tackles (38 solo), four pass deflections, two interceptions, and a sack in 14 games and 14 starts.
[19] Throughout training camp, Alexander competed against rookie John Johnson for the job as the starting strong safety.
[35] Defensive coordinator Wade Phillips demoted Alexander in Week 5 and named rookie John Johnson the starter in his place.
On October 9, 2017, the Rams released Alexander after he struggled in the first four games of the season and earned the 73rd highest overall grade among 83 qualifying safeties from Pro Football Focus.