Dear David Stern:

You blew it.

I’m sure you don’t see it that way. I bet you think you’ve laid down the law harder than Mardy Collins threw J.R. Smith to the floor with all the suspensions after that brawl between the New York Knicks and Denver Nuggets.

Carmelo Anthony is the leading scorer in the league, and you knocked him down for 15 rounds (OK, games) for that sucker-punch that he threw. Just shows you’re not afraid to discipline a star, right?

OK, how about a coach?

Make that two coaches.

Please, don’t even start about that $500,000 fine to both teams. Neither coach will pay a penny, and the franchises probably will find a way to write it off as a tax deduction.

Whatever sentence you delivered to Anthony, the same should have applied to Knicks coach Isiah Thomas. My ruling would have been 10 games for Anthony, 10 for Thomas.

Instead, it was 15 for Anthony, and a nod, and a wink along with a warning of “don’t do it again” to Thomas.

As for Nuggets coach George Karl, he should have been suspended for at least one game, or at least heavily fined.

At some point, can’t one of these millionaire coaches with their five assistants and their endless monologues about how to play the game the right way act like an adult when the pressure is on?

Did you catch some of the comments Monday?

Karl was calling Thomas a “jerk . . . jackass . . .” and some stuff that kept the TV censors busy. Thomas was talking about “class,” and Karl putting his players “in a very bad position.”

Forget the players, let’s put the two coaches in the ring and let them embarrass themselves. Karl is 55, Thomas is 45. They have been in the pro game for more than 50 years combined. After 100 years on this earth this is the best they can do?

Just as much as the fight, the conduct of your coaches brings shame to your league. You’ve fined coaches for criticizing officials and other offenses far less severe than this, but you suddenly came down with a case of judicial constipation when trying to figure out what to do with Thomas and Karl.

You wimped (or lawyered) out, and you’re smart enough to know that.

You’re the commissioner of the NBA; had that job forever. You know what really happened in Madison Square Garden the other night.

The game began with two coaches who can’t stand each other.

Karl loathes Thomas because the current Knicks coach has been ripping former Knicks coach Larry Brown.

Larry Brown happens to be a friend of Karl’s, as they both bleed University of North Carolina blue. Karl hammered Thomas to reporters a few months ago about Thomas not showing respect to Brown. Thomas didn’t appreciate that.

With less than two minutes to go in the game, the Nuggets were ahead by 19 points. Karl had four of his starters on the floor – just protecting his lead, he insisted.

The Nuggets said he had nearly all of his starters on the court at the end of what became an easy victory over the Atlanta Hawks a few weeks ago. If it wasn’t intentional to run up the score on Thomas, then it was not exactly a brilliant coaching move. Forget the fight, who would want the NBA’s leading scorer turning an ankle in the final two minutes of a game his team leads by 19 points?

Somehow, I think Karl is smarter than that. Somehow, there was another agenda here. Somehow, I bet you know it, too.

Dear Commissioner, the franchise in your home town is a mess.

It’s coached by Thomas, whose record since he stopped playing is a study in incompetence. He was overmatched as a general manager with the Toronto Raptors, nearly ran the Continental Basketball Association out of business and then took a terrible situation in New York and made it deplorable as the Knicks’ GM.

He’s coaching because owner James Dolan told Thomas that because he collected these overpaid underachievers, he now can coach them.

You must remember Thomas from his days in Detroit. You remember all the stunts that he pulled with the Bad Boys, starting fights with his mouth, then hiding behind the likes of Rick Mahorn and Bill Laimbeer.