The indictment of a US football star this week for allegedly organizing illegal dog fights has put the spotlight on the bloody, booming pastime that is attracting an increasingly wide following.
The blood sport that often uses pit bulls trained to fight is illegal in all 50 states, but can be found across the country.
"The phenomenon is increasing. It was very prevalent in the South now it's all over, in Chicago, New York, Baltimore, New York, big in Indiana, big in Wisconsin," said Michael Roach, director of field service and investigation for the Anti-Cruelty Society of Chicago.
"There are three levels of dog fighting: the street fighting level where other crimes are involved such as drugs, weapons, the hobby level and the professional level," Roach told AFP.
Bets can reach 20,000 to 30,000 dollars for bouts organized on the street and up to half a million dollars for more elaborate dog fights overseen by illegal breeders. There are some 20,000 to 40,000 dog fight fans in the United States, who operate underground and use the Internet to help organize events.
On Tuesday, Atlanta Falcons star quarterback Michael Vick -- the second-highest paid player in the National Football League -- was charged by a federal grand jury with having trained and provided animals for dog fights since 2001.
As part of the dog fights allegedly staged by Vick and his associates, losing dogs were sometimes drowned, hung, shot or electrocuted, according to the US Justice Department indictment.
Some 66 dogs, including 55 pitbulls, were founds on Vick's property in southern Virginia, with many of the animals chained to cars close enough to agitate each other but too far away to bite -- a common tactic to prepare the dogs for combat, experts say.
If convicted, the football star faces a possible six year prison sentence and 350,000 dollars in fines.
"It does go with the gang culture, in every urban area," said Laurie Maxwell of the Humane Society.
In recent years, animal shelters have been "inundated" with injured or scarred pitbulls, she said. The wounded animals account for 30 percent of dogs at animal shelters nationwide and 75 percent in US cities, according to Maxwell. Rescued fighting dogs have to be euthanized as they are too aggressive to be pets.
In city neighborhoods dominated by gangs and drug crime, people use pitbulls to intimidate residents and gangs steal dogs -- even sometimes cats -- for fights.
Fights take place "in abandoned buildings, basement, garages, warehouses, even in apartments where they used the doors to block a doorway and build a pit," Roach said.
"They use treadmills to train a dog to run and to develop their stamina they hang a rabbit or cat in a bag above the dog."
A study by Chicago's Anti-Cruelty Society said 40 percent of primary school children in the Chicago area have seen animal fights or know about them.
A dog fight can last anywhere from 15 minutes to five or six hours, until one of the dogs locks his jaws around the neck of the other and refuses to let go.
Then, "they use a break stick in their mouth to pull them away and release them again against each other," Roach said.
The dogs who lose are "often killed, set on fire with gasoline, electrocuted, shot, put on a railroad track.
"They are sending a message to others, saying, 'This is what happens to losers.'"