Seems like 10-20% of the student athletes would leave before a fifth year of eligibility would be used up, if not more, if you count attrition along with leaving early for the NFL. After everything plays out, it would just become an associative property maneuver. The same number of student athletes will stay five years.

None would be penalized for playing early, and that would free up coaches to ease players in any time they are ready, or the players are needed, creating no huge dilemma. After all, most tFr. won't be ready to play their first year on campus, and the ones who are, will probably leave after 3 or 4 years anyway.

Most players will suffer an injury or two, and if it is really bad, let them apply for that rare 6th year. This would cut out on a lot of "paper work" and monitoring.