[8] Throughout training camp, Mager competed against Steve Williams, Chris Davis, Greg Ducre, Richard Crawford, Manny Asprilla, and Lowell Rose.
[9] Head coach Mike McCoy named Mager the fifth cornerback on the Chargers' depth chart, behind Jason Verrett, Brandon Flowers, Patrick Robinson, and Williams.
[10] On September 20, 2015, Mager made his professional regular season debut in the Chargers' 24–19 loss at the Cincinnati Bengals.
[12] On December 24, 2015, Mager earned his first career start and recorded a season-high four combined tackles during a 30–14 victory over the Miami Dolphins.
[13] Mager entered training camp in 2016 competing against Casey Hayward and Jahleel Addae for the job as third cornerback.
Mager was named the fourth cornerback in the depth chart to start the regular season, behind Verrett, Flowers, and Hayward.