It's the NCAA graduation rate requirement. Everybody who gets athletic aid is to graduate within (I think) 5 yrs. If enough don't, then the team is ineligible for the postseason. Each year gets a score, and postseason eligibility is based upon a 4-yr average.Maybe everyone else knows, but can you enlighten me further on APR? I've seen it mentioned on a rare occasion, but never took the time to ask.
Of course it's more complicated than that -- APR means academic progress, so I think each guy also needs to complete a min # credits each year. If he quits the team, he still counts. If he transfers, IIRC he's a zero score for his first team (because he's no longer on track to graduate there), until he actually graduates somewhere.
Anyway, giving some athletic aid to guys who are very likely to stay and graduate on time (the guys who know accept being depth) is smart risk mitigation, and it helps keep those guys happy.