NBA - Illegal Defense

Could someone offer a coherent explanation of what is known in the NBA as “illegal defense”?

I know zone is not allowed, but how do teams get away with double- and triple- teams, etc.? When illegal defense is called, what has typically happened?

Thanks in advance…

Gosh, why don’t you ask something easy.
There are a lot of ways for a defense to be illegal. The easiest way to get called for it is for a defender to be standing in the key for three seconds with absolutely no defender around him.
I think you can find info on this on
There are rules which limit the number of defenders who can be on one side of the court if the ball isn’t there.
There are also little hash marks on the court for the officials to monitor to see where players are standing.

The zone defense has been illegal in the NBA since it started in 1946. The rules about it get tweaked a lot as coaches figure out ways to circumvent the prohibition.

Double- and triple-teaming are not illegal defenses.

To really confuse things, a team can also be called for an illegal offense.

To be precise you can go to and read Rule No. 12.
It might not be cogent, but that’s the actual rule.

My Gawd… I just read rule 12 on illegal defenses… And I used to think that Quartback Rating caclulations were the most complex item in professional sports. I was wrong. I’ve read legislation that was less confusing…

No wonder they want these guys to go to college. This thing reads like the infield fly rule as interpreted by the Supreme Court.

Thanks, BobT, but as you hinted, I may need to study this for a while.

I just checked out that link. Whew! And I thought I knew Illegal Defense pretty good.

Here are two situations where illegal defense is called.

  1. Lakers set up on defense as the Pacers come up court. Shaq stands inside the key on the weakside of the court (the side where there are only two players on offense). The The Pacers keep the ball on the strong side of the court (say with Miller, Jackson, and Davis). O’Neal has to be guarding one of those guys if he is standing in the key. If he isn’t and he stands in the key for three seconds. He’s illegal.

  2. The Lakers bring the ball upcourt and Rice stands outside the three-point line. Whoever is guarding Rice has to come out above the free throw line to guard him. If no one is, then it’s illegal defense.

If you want to see a Shockwave demonstration of this, try

The easiest way for me to describe the “illegal defense” call is thus: Defenders must either be guarding another player, one-on-one, or may be double-teaming (or triple- or quadruple-) the player WITH THE BALL. Guarding nobody or double-teaming away from the ball for 3 seconds constitutes illegal defense.