Physical Ability and Pedigree
Linebacker is a difficult position for high school players to transition from high school to college. It's why you rarely see freshmen making major impacts unless they are in special situations or do one thing well. Shawn Murphy is physically ready to play and was one of the top players coming out of high school. If you've been reading my work long enough, you know I don't put a ton of stock in recruiting rankings in general because I believe they are inherently flawed.
I'd much rather turn on the game tape and draw my conclusions, as opposed to looking solely at what a guy's ranking might be. Physical stature, or lack thereof, is usually a barrier to young linebackers getting on the field early. A lack of coaching at the high school level is another often high school coaches telling their best athletes to find the ball and make a tackle. College offenses are much more dynamic, and linebackers have more things to learn and identify. Murphy is 6'2" and 225 pounds and was the No. 72 player out of high school.