Carnifax, a three-star recruit from Warren, Oh., is the fourth-highest rated player in Northwestern's (incomplete) 2016 class, per 247 Sports.
NCAA rules allow athletes who have completed high school degree requirements to sign a Tender of Financial Aid, graduate early from high school and enroll in college in the winter or spring. Enrolling early allows athletes to get a head start academically and participate in spring practice.
Because Northwestern is on the quarter system, Carnifax will start school in Evanston winter quarter, and will take classes in the winter and spring before his classmates arrive in the summer.
The rest of Northwestern's class will sign letters of intent on Wednesday, Feb. 3, which is national signing day.
Carnifax is the second player to enroll early at Northwestern under Pat Fitzgerald. The first was Parrker Westphal, a member of the recruiting class of 2014, who enrolled for winter quarter of the 2013-14 school year. Injuries forced Westphal to redshirt his freshman year though, and he has seen the field only sparingly as a redshirt freshman.