[2] Sources: As a freshman at Purdue in 2010, Allen recorded 73 total tackles, 3.5 tackles-for-loss, one sack, three interceptions, two pick-sixes, and seven passes defended.

[18] On September 2, 2014, the Falcons signed him to the practice squad and retained five cornerbacks on the active roster, including Desmond Trufant, Robert Alford, Wilson, McClain, and Arenas.

[19] On December 16, 2014, the Falcons promoted Allen to the active roster after fellow defensive back Robert Alford was sent to injured reserve.

[22] Entering organized team activities, the new Falcons' coaching staff opted to move Allen from cornerback to safety.

The change was due to the Falcons failing to secure a new free safety to replace Dwight Lowery and to give Allen a better opportunity to make the active roster.

[25] In Week 3, Allen recorded seven solo tackles before leaving the Falcons' 39–28 victory against the Dallas Cowboys in the third quarter after sustaining a knee injury.

[26] On November 1, 2015, Allen recorded six combined tackles and made his first career sack on quarterback Jameis Winston during the Falcons' 23–20 loss against the Tampa Bay Buccaneers.

[29][30] Allen entered training camp slated as the starting free safety, but saw minor competition from Robenson Therezie for the role.

[34] The Falcons finished the 2016 season first in the NFC South with an 11–5 record, clinching a first round bye and home field advantage through the playoffs.

On January 14, 2017, Allen started in his first career playoff game and assisted on two tackles, deflected a pass, and returned an interception by Russell Wilson for 45-yards during the Falcons' 36–20 NFC Divisional Round victory against the Seattle Seahawks.

[35] On February 5, 2017, Allen made seven combined tackles in the Falcons' 34–28 overtime loss in Super Bowl LI to the New England Patriots.

[37] Defensive coordinator Marquand Manuel officially named him the starter, alongside strong safety Keanu Neal, to begin the regular season.

[38] On September 25, 2017, Allen recorded three combined tackles before leaving the Falcons' 30–26 victory at the Detroit Lions in the third quarter after suffering a concussion.

On February 13, 2018, Allen recorded four solo tackles in the Falcons' 15–10 loss to the eventual Super Bowl LII Champions, the Eagles in the NFC Divisional Round.

[52] On March 3, 2022, Allen joined Mike McDaniel's inaugural Miami Dolphins staff as a special teams assistant.