The rule's explanation takes up nine pages in the NBA official's manual. Violations have cost the Jazz 22 technical fouls this season as many as Karl Malone and Frank Layden together. Broadcasters wish they never had to explain the thing, and players are happy there are no written tests on the subject.

"It has something to do with quadrants and where your man is . . . who knows?" says Jazz rookie Bart Kofoed, bravely trying to describe the rule. "To me, it's very confusing."He's not the only one. Welcome to the NBA's illegal-defense rule, roughly as easy to understand as the new tax laws and full of almost as many loopholes.

The NBA has always outlawed zone defenses guarding an area of the floor, instead of a man by the logic that giant centers would dominate the game too much if allowed to roam around and the 24-second shot clock places enough pressure on the offense. Through the years, the no-zone idea has evolved into the latest rule, adopted in 1981 after Cotton Fitzsimmons, Don Nelson and Dick Motta holed up in a room and came up with the guidelines.

Previously, there was the defensive three-second rule to keep players out of the lane and the three-foot rule, forcing a player to stay within three feet of his man, no matter where he was on the court. Jerry Sloan, the Jazz assistant coach, remembers how the Lakers would send everybody else away and give the ball to Jerry West to go one-on-one with nobody allowed to help Sloan. "That was really ugly," he says.

The modern rule actually gives reasonable freedom to the defense. "We didn't want the big man just standing in the middle," said Matt Winick, the NBA's director of game operations, "but we don't want to take away the creativity of the defense."

Which brings us to what the defense can do, commonly misunderstood:

Any defender can leave his man to double-team the player with the ball, or pick up a man left open by a double-team. That legalizes the Jazz's halfcourt trap and the rotation defenses used by Milwaukee and the Lakers, among others. An offensive player can stand at halfcourt and yell "Zone" all night, but if his defender is aggressively double-teaming and not floating somehwere in the middle between his man and the ball, he's completely legal.

If a defender's man is below the free-throw line on the side of the ball, he can even double-team a player without the ball. And there's a new illegal-offense rule this season, preventing more than two players from standing beyond the top of the circle on the weak side.

While the Jazz's halfcourt trap was labeled a "matchup zone" by Seattle Coach Bernie Bickerstaff, the Jazz are actually called more frequently for violations in their regular defense as players lose their men. The trap just looks more like a zone, because players are left open.

"As long as you're moving and staying active, you're OK," says Sloan.

The rule does require players who are not double-teaming to:

Stay within the middle or upper boundaries, or drop down for no more than 2.9 seconds. When his man is above the free-throw line, the defender can go no lower than the middle area. When his man is above the top of the circle, the defender must be in the upper area.

Follow his man to the crossing point on a switch. When two offensive players cross, the defender can't just switch men and wait for the other to come to him. That's what Layden means when he frequently yells, "They didn't come together."

Those are the basics of the rule, which causes trouble for broadcasters, coaches, players and even referees.

"You think you're illegal and you're legal," says Kofoed. "You think you're legal, and they call it. That's the puzzling part about it."

How about spectators, then?

"Only the die-hard NBA fans will understand it," says Jazz broadcaster Rod Hundley. "I'd say 80 percent of the people have no idea what it is."

When Layden joined the CBS crew for a telecast of the NBA Finals last June, he was invited to offer ideas in a production meeting. He suggested a halftime segment devoted to educating the viewers about the illegal-defense rule. "Nobody in the room wanted to do it, because they didn't understand it," he says.

Chick Hearn, the legendary Laker broadcaster, once did have NBA referee Darell Garretson explain the rule. Even Hearn admitted, "I think I know this game pretty well, but there's a lot of that I didn't understand."

One coach suggests that referees are instructed to call the violation less, to avoid breaking the flow of a broadcast and putting pressure on network announcers.

As for the referees, basketball guru Pete Newell once told Sports Illustrated, "There are a lot of people involved who don't understand the guidelines, and a lot of them wear whistles."

Historical note: Layden drew the first technical foul that eventually led to the famous $10,000 fine in Denver because he called out "Illegal defense" to referee Jack Madden.

"The illegal defense has to be called, if it's blatant," says the NBA's Winick. "You're not standing out there looking for that and nothing else. That doesn't mean we let them go, but there has to be some judgment involved."

The first illegal-defense violation carries a warning; the Jazz are warned in almost every game. Subsequent violations result in technicals, and the Jazz were tied with New York, a pressing team, for the NBA season lead at last check.

"I have a problem with the inconsistency of the calls," Layden said, "but I think the officials are handling it well. They're not overdoing it."

Says the Jazz's Mark Eaton, "They're not going crazy with the technical aspects of it."

Thank goodness. The thing is tough enough to figure out already.