The NCAA continually fails to address the rot in college sports, despite a 400-page phonebook-sized manual.

There are rules to govern tweeting, rules about “normal retail cost,” and even rules for parking, yet none of them are able to curb Lane Kiffin’s mouth, John Calipari’s ambition or Derrick Rose’s grade inflation.

They’re all nonsense, and it’s time to throw them out. The NCAA needs only one good rule. It’s a rule that would clean up a lot of the mess instantly because it would restate the priority of college athletics: Make freshmen ineligible.

Amazing, how that one rule would solve so many problems. For instance, it would solve Lance Stephenson’s nagging little dilemma.

Stephenson, arguably the nation’s most overprized high school basketball talent, would have to decide whether a scholarship is a priceless gift or an unwanted obstacle; he’d have to either commit to an education or forgo the charade and play a year in Europe, where he could learn to insult his teammates and coaches in a foreign language before he skips to the NBA and becomes Commissioner David Stern’s latest ward.

If freshmen were ineligible, it would help clear things up at Memphis, where Calipari’s combination of slick and slack has left the program facing major penalties over Rose’s academic records.

Make freshmen sit, and some of the systemic fraudulence by which they are pushed along might go away. High schools would have less incentive to falsify athletes’ grades and more incentive to actually prepare them.

Make freshmen sit, and it might lessen the corrupting influence of sneaker company reps.

Make freshmen sit — an idea advocated by Bob Knight, Dean Smith and Lou Holtz — and million-dollar head coaches might regain some perspective and remember they’re just gym teachers, and that their competitive pressures or problems don’t come ahead of the university’s purpose.

And the most important reason to make freshmen ineligible: because it would be a clear statement that the NCAA is a nonprofit that puts education ahead of business.

Freshman ineligibility was a healthy, time-honored policy in American collegiate sports from the turn of the century until 1971, when the NCAA voted it down. The reason? Money.

Member schools no longer wanted to house, feed and educate players who weren’t bringing in trophies or revenue.

The difficulty of reconciling sport, education and commerce has plagued campuses since Rutgers and Princeton played football in 1869, and Rutgers fielded three freshmen who were failing chemistry.

The trouble is, over the years the rulebook has steadily tilted in favor of commerce. The rulebook is not about enhancing education or enforcing clean competition, it’s about enforcing competitive balance and profit-sharing.