Pimps will traffic thousands of under-age prostitutes to Texas for today's Super Bowl, hoping to do business with men arriving for the big game with money to burn, child rights advocates said.

The country's largest sporting event, the game between the Green Bay Packers and the Pittsburgh Steelers will make the Dallas-Fort Worth area a magnet for business of all kinds, including the multimillion- dollar, under-age sex industry, said activists. Authorities are trying to combat the annual spike in trafficking of under-age girls that coincides with the game.

"The Super Bowl is one of the biggest human trafficking events in the United States," Greg Abbott, the attorney general for Texas, told a recent trafficking prevention meeting. Up to 300,000 girls between 11 and 17 are lured into the US sex industry annually, according to a 2007 report sponsored by the Department of Justice and written by the non-profit group Shared Hope International. Some 90 per cent of runaways and children whose parents force them to leave home fall into the trade and are often beaten, drugged, raped or imprisoned to force compliance, said the report.

Pimps tattoo girls with dollar signs or the word "Daddy", and take them to unfamiliar cities where they are more vulnerable.

"At previous Super Bowls, pimps hired cab drivers to turn their vehicles into mobile brothels," said Deena Graves, executive director of the child advocacy group Traffick911.

"We are expecting thousands of under-age domestic minors to be trafficked to the Super Bowl," said Nancy Rivard, founder of the non-profit Airline Ambassadors International. Non-profit groups working at the 2010 Super Bowl in Miami supplied the figure, she said.

Law enforcement agencies and advocacy groups rescued around 50 girls during the previous two Super Bowls, said Graves. Six were registered on the Center for Missing and Exploited Children website. One had been trafficked from Hawaii.

To fight the trade, authorities, child welfare advocates and the airline industry are collaborating. Representatives from American Airlines, Delta, United, Qantas and American Eagle are holding a training session to help them spot signs of trafficking. Rivard will also work with another 100 flight crews to distribute materials on flights.

Some 67,000 people signed a petition on www.change.org opposing sex trafficking as part of a campaign by Traffick911 called "I'm Not Buying It!".

The campaign has attracted heavy hitters such as the Dallas Cowboy Jay Ratliff, a three-time Pro Bowler, who made a public service announcement entitled "Real men don't buy children. They don't buy sex".

Girls who enter the grim trade face harsh treatment and danger, according to a Dallas police report in 2010. Few who emerge are willing to speak about it. Tina Frundt, 36, is an exception. Now married and living in Washington DC, Ms Frundt was lured into sex work at 14 after she fell for a 24-year-old who invited her to leave home in 1989 and join his "family" in Cleveland, Ohio. That family consisted of the man and three girls living in a motel. When Ms Frundt declined on the first night to have sex with her boyfriend's friends, they raped her. "I was angry with myself for not listening to him, so the next night when he sent me out on the street and told me... [to earn $500] I listened," she said in a telephone interview.

Ms Frundt paced the streets for hours and finally got into a client's car. When she came home in the morning with just $50, her pimp beat her in front of the other girls to teach them all a lesson and sent her back on to the street the next night with the warning not to return until she had reached her quota. The scenario was repeated night after night as Ms Frundt's pimp moved his stable across the Midwest. Any sign of rebellion led to further beatings. Escape seemed out of the question. "I was a teenager in a strange town with no money and no place to go," she said. She finally escaped by getting herself arrested.

Typically, pimps recruit unwitting girls at shopping centres, mall events and on the internet. Once ensnared, shame, fear and psychological manipulation make it hard for them to break free. Clients hook up with girls via the internet, through hotels, massage parlours, strip clubs and escort services, the report said.

Seconds of play, hours of razzmatazz

If you have never watched American football, tonight's Super Bowl will be as incomprehensible a spectacle as an Aztec sacrifice would have been to the Conquistadors.

The game will be played in an air-conditioned stadium with a roof, in warm and mid-western Arlington, Texas (home ground of the Dallas Cowboys). From the roof are suspended the world's biggest HD video screens, each 60 yards long, so that the crowd in the stadium can see what's happening in close-up and watch the replays, essential to understanding the intricately choreographed brawl.

Although the rules change every year to make the game safer or more exciting for television (the latest change is a ban on hitting an opposing player helmet-first), the basics are simple.

The aim is to take the ball to the end zone of the 100-yard-long field. The team with the ball is allowed four attempts to advance 10 yards. Play stops every time the ball carrier is brought to the ground. If a team gains 10 yards, they start again with another four attempts. If they fail to gain 10 yards in three attempts, they usually use their fourth to kick the ball as far down field as they can.

There are two basic kinds of play:a run or a pass. For a pass, the quarterback, the leader of the offense, usually throws the one permitted forward pass. Look out for running back James Stark and wide receiver Antwaan Randle El.

By coincidence, today's evenly matched teams, the Green Bay Packers and the Pittsburgh Steelers, have a history in the game's rust-belt origins and are the only remaining working-class names in the league. The team from Green Bay, a port on Lake Michigan, was founded 92 years ago, sponsored by a meat packing company. But today's game would be as unrecognisable to the meat packers of inter-war Wisconsin as it would be to most Brits.

The players – 45 on each side since the introduction of unlimited substitutions – are in action for a few seconds at a time. Ninety minutes of playing time will take three-and-a-half hours in real time.

The half-time show, meanwhile, has become a grisly index of music-industry has-beenery, today featuring the Black Eyed Peas.