DANVERS - The 2007 Danvers Invitational Soccer Tournament involves nearly 400 soccer games, five fields and as many as 3,000 kids, their coaches and parents. At the Danvers High site alone, games were going on yesterday simultaneously on the soccer fields, the baseball field and the football field.

In between, kids and parents waited, sometimes bouncing soccer balls around, sometimes sneaking off for fried dough. It's an amazingly well-organized event. "I'm envious," marveled parent Brian Cohen from Marblehead. "I wish we could put something like this together in Marblehead."

Yet, given the sheer numbers, with teams from all over the North Shore and beyond, you would expect that something's got to go wrong. Someone is going to be berserk over a bad offsides call or an undeserved penalty card.

"There's always problem people," conceded Janet Gargan, one of the organizers.

Even so, Gargan can't remember any serious issues at this annual event, and the policy of "zero tolerance" for heckling referees might be one reason why. The rule has been in place now for five years, and it outlaws things that might seem innocuous - like shouting, "Ref, you missed that one."

But it works, said Bob Gabel, another official. "It gets the parents in the right attitude."

If a situation gets out of hand, added Gargan, "People are spoken to. Usually that will resolve it."

Zero tolerance means simply that no one is supposed to address the referees during the game. Questions can be raised at half time or after the game. Salem native Jerry Morin, the head of referees, has been working the tournament since 1985, and he knows the reasons for such a rule.

"It's a very passionate sport," he said. And it's not always the players who get the most passionate. "The kids come to play the game. They may be unhappy with the calls. But usually when the game ends they're on the swings five minutes later."

Morin hastens to add that the vast majority of adults behave well, too. But the zero-tolerance policy is meant to protect the referees. Some are as young as 14, and when they find judgments questioned by adults - even in mild terms - it can be unsettling for them.

"Zero tolerance puts the onus on the coaches to help control themselves and the parents," Morin said. People can be asked to quiet down or even to leave the area. In a worst-case scenario, a ref can simply stop the game. "This is a tool that's useful for the younger referees."

Above all, Morin wants to keep the young refs coming back and learning the job, which pays from $20 to $60 a game.

Older referees, Morin acknowledged, sometimes "go deaf" when the noise level grows, deciding to let the loudmouths let off steam. Veteran referee Angelo Cassanelli of Haverhill, originally from Italy, takes the noise in stride. He laughed, recalling a plan to hand out lollipops to the parents. "As long as they're sucking on those lollipops they won't be able to yell."

Parent Libby Kellard of Peabody has worked as a "field marshal," helping to keep parents under control. It's another case of heading off trouble - with the result she can't remember any serious problems. Her husband, Bob, is a coach. "And he doesn't take (the score) too seriously."

"Most parents know you don't yell at the ref," agreed Oliver McConnell, also of Peabody, as he watched his high school-age son play goalie. It can be a serious matter, he added, remembering the "hockey dad" whose rage in 2000 led to a fatal confrontation at a Reading ice rink. "It's OK to yell. But you can go over the line."

Parent Heather King of Amesbury has no problem with the policy. "We're a hockey family," she smiled while unloading equipment and her son from a van, "so we believe in zero tolerance. ... I believe it's a tough job. And parents need to let the referees do their work."