Clark, a 6-2, 244-pound redshirt freshman, arrived on campus Aug. 18 and went through his first full day with the Demons Aug. 19.
He is eligible to play immediately, said head coach Jay Thomas.
The Demons also added Nick Fabrizio, a transfer from Navy who will sit out the 2015 season as a redshirt and will have three seasons to play. Fabrizio, a 5-11, 190-pound option quarterback from Valrico, Fla.-Durant HS, is the son of former Demon quarterback Rob Fabrizio (1984-86) and brother of junior linebacker Robert Fabrizio.
Clark was a standout at O. Perry Walker High School who made 111 tackles, including 17 for lost yards, nine sacks, nine forced fumbles and two interceptions as a senior in 2012.
He redshirted last year at Louisville, and was listed as the second-team middle linebacker for the Cardinals entering preseason camp.
He was rated a three-star prospect by 247Sports.com and a two-star recruit by ESPN.com, Scout.com and Rivals.com as a senior.
He was ranked as the nation’s No. 57 inside linebacker by 247Sports.com after starring for coach Emanuel Powell, earning honorable mention all-state and first-team all-district honors along with making the Times-Picayune’s All-New Orleans Metro team.
Clark sat out the 2013 season as a redshirt under Louisville coach Charlie Strong, now at Texas, then went through spring practice and took part in a few preseason workouts earlier this month under the new Louisville staff headed by Bobby Petrino.
Fabrizio attended the Naval Academy Prep School in 2012-13. At Durant Senior High, he was All-Hillsborough County in the Tampa Bay metro area as a senior, when he ran for 1,085 yards and 19 touchdowns on 129 carries, averaging 8.4 yards per run.
He also threw for nine touchdowns and 733 yards on 49 of 97 aim under coach Mike Gottman.
He led the Cougars to the 2011 district championship, their first since 2003, and was the East MVP in the Hillsborough County Senior All-Star game after throwing for a touchdown and running for two.
“These are two quality young men who will help our team. Lyn fits the mold of what we want in a linebacker and should be able to make an impact this season,” said Thomas. “Nick will add an interesting dimension to our quarterback position next year.”
The Demons adjusted their practice schedule for today, shifting to 8 a.m. workouts and out of the heat of the mid-afternoon. Aug. 24, NSU will practice at 7 p.m.