With the first weekend of the season over, fantasy football fans are either celebrating an early victory or licking their virtual wounds this week -- and college athletes are no exception. More than 70 percent of National Collegiate Athletic Association athletes participate in fantasy leagues.

The problem: Many of those athletes violate NCAA rules by doing so.

Twenty percent of NCAA athletes admit to participating in fantasy sports leagues with entry fees and cash prizes, according to a survey conducted last year by the NCAA. All but 1.8 percent of those athletes were men. More than 80 percent of athletes said they didn't realize joining a paid fantasy league was an NCAA violation. The survey's results were based on a representative sample of 23,000 students across 22 sports in all three divisions. If the survey included all NCAA athletes and the percentages held, the number of players violating the rules by entering paid fantasy leagues would be about 90,000.

Citing mental, health, and safety issues, the NCAA forbids sports gambling of all types. Students can too easily become addicted to gambling, the NCAA states, and can be viewed by "organized crime and professional gamblers as easy marks for obtaining inside information or affecting a game’s outcome." While gambling among college athletes has decreased in recent years, participation in sports wagering and fantasy leagues has gone up.

In 2013, the NCAA described the overall growth of sports wagering as "explosive."

Fantasy sports (a game where players build a virtual team of athletes and compete against each other based on statistics created by how the real athletes perform) have also exploded in popularity. More than 40 million North Americans now play fantasy sports, according to the Fantasy Sports Trade Association. They spend $15 billion per year on league-related expenses. Football is the most popular fantasy sport, and in 2013, $1.6 billion was spent in fantasy football leagues. Four years earlier, that number was just $800 million.

"Fantasy leagues are very popular among college-age students," said Jeffrey Derevensky, co-director of the International Center for Youth Gambling in Canada and a frequent author of NCAA studies about gambling. "The number of fantasy leagues are growing. Americans in particular are very much interested in college sports and athletes in general are really interested in other athletes. A lot of fantasy leagues are done right on campus. They don't have to go to a casino to get involved in a fantasy league. That makes fantasy sports an attractive thing for them."

Though the entry fees for the types of leagues many students join are typically small, the sanctions can be tough.

A college athlete participating in a league involving his own team or university -- and there are college fantasy leagues -- could permanently lose his eligibility as an NCAA athlete. An athlete participating in any paid league could sit out an entire season.

"The penalties are based on the circumstances of each case and the penalty guidelines set by each division," Emily James, associate director of public relations at the NCAA, said. "Fantasy sports league cases involving student athletes are processed by our student-athlete reinstatement team. Fantasy sports league issues have also been processed as secondary and major violations by our enforcement team."

So why do so many athletes enter paid leagues despite the risk?

Part of the reason is that many athletes don't think of fantasy sports as gambling. And, legally, it's not. Under the Internet Gambling Prohibition and Enforcement Act of 2006, fantasy sports are defined as a game of skill. But James said the NCAA considers fantasy sports to be sports wagering, as it defines sports wagering as "putting something at risk with the opportunity to win something in return." It doesn't matter if the athlete is paying a large fee to join a league on a website or $5 to join a league in his friend's living room: if there's money on the line, it's an NCAA violation.

Even some coaches and administrators don't realize that playing in paid fantasy leagues is against NCAA regulations, Rachel Newman Baker, the NCAA's former managing director of enforcement, said in a statement last year.

“Above almost anything else, a typical student-athlete does not want to negatively impact his or her team,” said Newman Baker. “Considering that roughly 40 percent of males think their coaches see sports wagering as acceptable, programmatic efforts to educate need to involve not only student-athletes, but also coaches and administrators.”

In 2010, the University of Missouri at St. Louis was placed on two-year probation after the head coach of its men's golf team played in several fantasy leagues with entry fees as high as $1,300. The coach eventually purchased and operated his own fantasy football operation, recruiting a volunteer coach and three of his players to act as commissioners, all while still a golf coach at the institution. Secondary NCAA violations have involved athletic department spokespeople, assistant coaches, and facility managers paying between $30 and $100 to join fantasy leagues.

In the Missouri case, the NCAA cited a lack of education as one of the main drivers of the misconduct. It's a problem, the association says, that extends to many universities and athletic departments.

A quarter of Division I athletes say they have not received information about NCAA gambling rules, according to NCAA surveys. In Divisions II and III, nearly half of the athletes say they haven't been told about the rules. The number of students who have received information about rules concerning fantasy leagues specifically is likely even lower because most officials don't see fantasy sports participation as a student health concern like they do more stereotypical forms of gambling like wagering on sporting events and horse racing, which can more easily lead to addiction, Derevensky said.

"It's against NCAA regulations, but most kids who have gambling problems don't get involved in fantasy leagues," he said. "Most individuals who have gambling problems can't wait that long to find out what the results are going to be. The concern about gambling from a student athlete perspective involves the health and well-being of the athlete, and the integrity of the game. So the NCAA is trying to educate students about gambling in general."