It's not difficult to understand why Tim Donaghy, the rotten ref, is offering unsavory information about NBA officiating.

It's not difficult to understand why the media and the public are ready to give at least some credence to Donaghy's assertions.

What is difficult to understand is why NBA commissioner David Stern is so smug in the face of Donaghy's charges leveled against the league.

Stern immediately began playing D when Donaghy, who is awaiting sentencing for gambling on games in which he officiated, claimed that a 2002 playoff series was rigged by referees and officials, and that the NBA routinely encouraged referees to call bogus fouls to manipulate games while also discouraging them from calling technical fouls on star players to protect TV ratings.

Stern immediately labeled the charges as baseless and insisted Donaghy was the only rogue referee. "... the accusations that we manipulate games that then get reported on ... the facts underlying those, they're false," Stern said. "We don't."

It would be easy to dismiss out of hand anything a convicted felon says — except that the NBA didn't catch Donaghy in the first place, the feds did. So where does the commish get off being so confident in his system of policing his officials in the first place?

When Donaghy was busted last year, Stern said that there had been nothing suspicious about the frequency of Donaghy's foul calls, his bank account activity or anything else that would have tipped off the league. After boasting that the NBA's system of monitoring referees gives the league the best officials in sports, he said he wasn't surprised Donaghy went undetected.

"If you're intent upon engaging in criminal activity," he said at the time, "and if you are acting alone in many cases without the knowledge of even your family, it's possible. Our history is replete with examples of that. So it doesn't come as a surprise that you could go undetected."

But now he's saying he knows for certain that the league is clean.

According to Stern, Donaghy, an NBA referee for 13 years, was rated in the top tier of officials.

But Stern is sure the rest of the refs are good to go. Fool him once, shame on him; fool him twice — couldn't happen.

The commish is certain he has a handle on the integrity of NBA officiating, but he didn't know about the eight referees who were charged with tax fraud in 1998. He didn't know they were downgrading first-class airline tickets purchased by the league and pocketing the difference without reporting the income to the IRS.

But he's sure he knows the rest of the referees are clean.

He didn't know about veteran referee Joey Crawford's personal feud with Spurs' star Tim Duncan until the ref ejected Duncan from a 2007 game against Dallas and, according to Duncan, challenged him to a fight on the court. Crawford was suspended for the rest of the season.

Stern also didn't know that Donaghy was engaged in wire fraud and transmitted wagering information and was taking cash payoffs from gamblers and making bets on games in which he was officiating.

The commish finally reluctantly agreed to launch the league's own investigation of Donaghy's assertions late last week, but only because of, as he acknowledged, the intense media coverage. Until then, he was indignant and defensive and clearly in denial, adopting the same stance as baseball commissioner Fay Vincent when the steroid allegations first began to surface in the Major Leagues. Remember how they scoffed at Jose Canseco?

Like Canseco's steroid accusations in baseball, Donaghy's assertions merely reinforce long-held suspicions by fans and media — the separate rules for star players, the alleged league plot to ensure that big-market teams win and so forth.

In the post-Donaghy era, everything looks even more suspicious — from Michael Jordan's pushoff of Bryon Russell to the "blown" calls on 3-point shots in Game 6 of the 1998 Jazz-Bulls NBA finals game to the New York Knicks winning the right to pick Patrick Ewing first in the 1985 NBA draft.

The NBA's huge credibility problem makes it crucial that the league investigate Donaghy's charges instead of stonewall tactics a la Vincent. Perception is everything, a point that seems lost on Stern and the NBA. They tried to ignore Donaghy's charges and hoped they went away, a method that has worked in the past. To wit: The Joey Crawford Case.

Crawford was one of those referees accused in the airline-ticket tax scandal. He was sentenced to six months house arrest and three years probation for tax fraud. He resigned immediately, but was reinstated after the NBA owners' lockout shortened the 1998-99 season and never missed a game.

In April 2007, after the altercation with Duncan, Crawford was suspended for the balance of the season and the playoffs. He was reinstated again this season.

Guess who was officiating during the controversial Game 4 matchup between the Spurs and Lakers last month when there was a crucial no-call in the final seconds on a play in which the Spurs' Brent Barry was fouled by Derek Fisher.

The following day, the NBA announced that a foul had occurred and should have been called. Crawford, the man who wanted to fight Duncan, was the closest official to the play in question. Not only is Crawford, a referee who has an open feud with one of the league's star players, still officiating in the NBA, he's officiating Spurs games — in the playoffs, no less.

Small wonder the NBA has a credibility problem.

Stern can't afford to ignore Donaghy.

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