Crude fan behavior has become an increasingly prominent feature of the contemporary sports experience, and it doesn't matter whether you're talking about baseball, football, basketball, soccer, or hockey. Nick Miller, 55, a management consultant in Concord who is involved in youth soccer, says, "I won't take my children to most professional sports events anymore because of what happens in the stands: swearing, drunkenness, and the level of riding the referees, umpires, and players."

It's not just the pros, however. Even at the high school or middle school level, once-unthinkable behavior now infects athletic contests. Just a few weeks ago, a 46-year-old hockey father from Hopedale was arrested for allegedly punching, kicking, and cursing a 10-year-old boy who played on an opposing team.

Doug Cross is a mild-mannered fellow, but he has had enough. So Cross has launched a crusade to change fan behavior. That may sound like a Sisyphean task, but Cross is convinced it's doable if he can get fans to think about their impact on the games they profess to love. He has started a website called Goodfans.com that offers T-shirts, wristbands, and bumper stickers for sale with the catchy, and pointed, message: "Good fans make good sports." The website is also a repository for news stories about fan misbehavior; let's just say it seldom lacks for material.

"The deterioration of the respect and tolerance of one another is taking all the fun out of the game," says Cross, 51, of Framingham, an instructional designer for a computer company. "Ninety percent of the fans are good fans, but it's the 10 percent of fans who can ruin it for everybody. It's like the bully in school who, by virtue of being the loudest and most obnoxious, gets all the attention. Going to a game, being surrounded by F-bombs, it spoils the experience."

Don't get him wrong: Cross loves sports. He is not trying, he says, to create a squad of "Fan Police." While GoodFans.com is a for-profit enterprise, he insists he is he not motivated by a desire to make money off the sale of T-shirts. (He says he plans to donate 10 percent of the proceeds to local youth programs that support good sportsmanship.) What animates him, he says, is his belief that fan misbehavior has risen to the level of a crisis, one that his website can help combat with awareness and education. To underscore the urgency of the issue (and the consequences if it goes unaddressed), Cross points to an episode that was, for him, the tipping point: the nationally televised brawl nearly three years ago between fans of the Detroit Pistons and several players for the Indian a Pacers, including Ron Artest. That brawl began when spectators added to on-court tensions by throwing beer and popcorn at the players, who waded into the stands and traded punches with fans

Fan misbehavior has always been part of sports. Cross's concerns actually go back more than three decades. He was 18 and making his umpiring debut in a girls' softball game. There was a close play at second, and Cross blew the call. He admits that. The base runner was safe. But was that any reason for a coach to run out to Cross and scream epithets in his face? And by what twisted logic did a teenager's fleeting moment of human error give fans a license to spend the rest of the game jeering and chanting at the team that had benefited from the blown call?

"Some of the girls were on the bench in tears," Cross recalls. "They didn't want to play." Thirty-three years later, the memory still prompts a slight shake of the head. "That was a real catalyst for me in understanding the impact fans can have on a game," he says.

More and more, he says, that impact is a negative one. Out-of-control fan behavior seems to be on the rise, and it is the one thing all sports have in common. Sometimes tragedy results. Twice in the past three years, raucous celebrations by local fans have ended in death. On Oct. 21, 2004, after the Red Sox won the pennant, tens of thousands of mostly young fans surged into Kenmore Square. In the chaos, Victoria Snelgrove , a 21-year-old Emerson College student from East Bridgewater , was fatally shot in Kenmore Square by Boston police. Earlier that year, on Feb. 2, after the New England Patriots won the Super Bowl, a crowd near Northeastern University flipped cars, threw beer bottles, and set bonfires. A drunk driver plowed into a crowd of revelers, killing 21-year-old James Grabowski of West Newbury.

At the high school level, perhaps no sport illustrates the decline in fan behavior more than the one whose growth has been so explosive: soccer. For several years, Cross coached his son's soccer team in Framingham. He now attends his daughter's games. He has seen how obnoxious fans can poison the atmosphere, sending what he believes is an unsettling message about acceptable behavior to impressionable youngsters. "They're seeing fans screaming at each other, screaming at officials," Cross says. "It's embarrassing, what's said on the sidelines."

Miller, the management consultant, is also the director of in-town soccer for the Concord-Carlisle youth program. Even though he and the coaches he supervises make it clear to parents that no verbal abuse of players will be permitted , adult fans think nothing of harshly criticizing the high school students whom the program trains to work as referees.

"We lose maybe a third to a half of the kids within a couple of years because of the grief they take from parents who question their calls or tell them they're blind," Miller says. "That's pretty tough for a freshman or sophomore to take."

As a former pitcher in the Cape Cod League (a collegiate summer baseball league) who now coaches club soccer, David Pennie has a dual perspective of fan behavior . There is no question, he says, that it has deteriorated over the years, especially when the games start to mean something. When the games involve young children, Pennie says, the competition is friendly and the fans are civil.

"But as you get up to the higher levels, the parents -- not all of them, but a lot -- their moods kind of change," says Pennie, 48. "It's almost like they're living their fantasy through being real competitive. It comes out real nasty. I've seen some nasty stuff, with fans yelling at my players or their own players. When their teams are getting outplayed, they turn to verbal abuse."

Is it possible to induce a sense of shame in such people, or at least self-awareness? Cross thinks so. In fact, he believes that restoring basic civility at professional ballparks and high school fields could be an important first step toward tackling the wider culture of rudeness and crudeness of which fan misbehavior is a promi n ent part.

"I really do believe that as a culture and a society we do have a civic responsibility regarding respect and tolerance for each other," he says. "We're just asking people to keep the big picture in mind regarding the greater implications of the way we behave."