Taken 17th overall in the first round of the 2014 NFL Draft out of Alabama—fresh off an SEC Defensive Player of the Year campaign and a BCS National Championship—C.J. Mosley entered the league with massive expectations. Step-for-step, he filled the void in the middle of Baltimore's front seven, bringing immediate stability, elite tackling, and pre-snap communication to the defense.

Mosley operated as the classic, physical middle linebacker built for AFC North football. Though he wasn't deployed primarily as an edge pass-rusher, his value lay in his downhill diagnosis and lateral range. Mosley possessed a knack for sifting through interior trash to bring down ball-carriers in the hole, while dropping into pass zones with natural spatial awareness to undercut throwing lanes.

Mosley burst onto the professional scene in 2014 as a rookie. He started all 16 games, recording 133 total tackles, 3.0 sacks, eight pass deflections, and two interceptions. His impressive debut earned him a spot in the Pro Bowl and Second-Team All-Pro honors, and he finished second in AP Defensive Rookie of the Year voting. He backed that up in 2015 with another 117 tackles, a sack, and a 41-yard fumble return for a touchdown against Denver.

Over three seasons, Mosley became a regular at the Pro Bowl. In 2016, he achieved a career-best four interceptions and made 92 tackles, earning his second Second-Team All-Pro honor and second Pro Bowl appearance. His 2017 season was possibly his best in Baltimore: he recorded 132 tackles, 1.0 sack, three forced fumbles, and two interceptions—including a 63-yard return for a touchdown against Miami—securing his third Pro Bowl and second Second-Team All-Pro selection.

In 2018, during his last year in Baltimore, Mosley recorded 105 tackles and delivered the season's defining moment in Week 17. As Cleveland advanced late in the fourth quarter, Mosley intercepted Baker Mayfield on fourth down, clinching the AFC North title for the Ravens. He concluded his season with his fourth Pro Bowl and fourth Second-Team All-Pro honors.

When Mosley hit free agency in 2019, he signed a landmark deal with the New York Jets, leaving a significant leadership void in Baltimore's linebacker corps.  Over his five years with Baltimore, Mosley started all 77 regular-season games he played, recording 580 combined tackles, 8.5 sacks, nine interceptions, six forced fumbles, and six fumble recoveries.