The Big Ten has closed the door behind anybody who walks through it. The new Big Ten basketball eligibility rule prohibits men's and women's players who left school to play professionally from holding onto their college eligibility. One sentence of policy. It answers a question that has been wobbling around the sport for two years.

Understand what it is actually aimed at. The old assumption was that turning pro was a one way street, and it was, because there was nothing back on campus worth returning for. That is not the world anymore. Between name, image and likeness money and revenue sharing, a fifth year in a power conference locker room can out earn a modest contract overseas or a developmental league deal. So the math flipped, and once the math flips, somebody tries the door. The Big Ten just bolted it.

I like the clarity more than I like the rule. Clarity is the one thing eligibility policy has not had in a while, and coaches building a roster in February deserve to know whether a kid who signed a pro deal in October is a phone call away from re-enrolling. But there is an honest counterpoint sitting right there: eligibility rules have spent the last few years getting dragged into courtrooms by athletes who did not care for them, and a conference bylaw is only as durable as the first judge who reads it. Bolt the door, sure. Somebody always brings a lawyer.

checked the almanac: in 1971 the Supreme Court sided with Spencer Haywood, and the pro league had to let him in before his college class graduated. the door between college and the pros has been argued over for fifty five years. it keeps getting decided by people in robes, not people in whistles.

What I do not have in front of me yet is the effective date or whether this is retroactive to players already gone, and I am not going to guess at either. That detail matters more than the headline does.

What I am watching next: whether the other power conferences follow inside the month, or whether the Big Ten stands alone on this long enough for a kid with a pro stub and a good attorney to test it.