Sense we all seem to be donating $.02, I'll do my part...
I am fairly sure that a player needs to meet two criteria:
1. Be in good standing with the university - as Zurp pointed out, this is the magical line that gives the OSU the ability to make up their owns minds about who gets retired.
2. Graduated - I didn't see this mentioned any where before in this thread, but I'm almost 100% sure that this is a requirement for getting your number retired as a Buckeye. I don't think it needs to be a graduate of OSU (in case of a transfer), but the player still needs a degree. Personally, I REALLY like this rule. How stupid would it be to hang a bunch of names and numbers of players who never made it through their college courses? The player doesn't even have an alma matter, but he has his number retired??? Obviously, this rules Pace out. Don't get me wrong, Pace was (still is) an incredible Buckeye, but he does not deserve to get his number retired.