Whether or not you have your amateur status depends on multiple factors. For Division I, II, and III sports, the NCAA reviews nine different aspects of an athlete’s profile to determine eligibility. Any violation of these nine factors may result in penalization or lose of eligibility with the NCAA.
Contracts with a professional team: Most of the time the NCAA will allow you to sign a contract with a professional team, as long as you're not receiving pay or benefits. However, they will closely review any contract you have signed with a pro team.
Salary for participating in athletics: To be declared an amateur, you cannot receive any salary for competing in athletics.
Prize money: The NCAA does not allow an athlete to earn money or prizes that are worth more than the cost of participating in an event. If you are not sure if your prize will violate NCAA rules, you are better off not accepting it.
Play with professionals: The NCAA will examine any time you have spent playing on a professional team or in professional competitions.
Tryouts, practice or competition with a professional team: If you have spent any time competing or trying out with professionals, regardless of whether you made the team or not, the NCAA will take a look at it to make sure you did not lose your amateur status.
Benefits from an agent or prospective agent: Amateur athletes may not have an agent. Sometimes agents try to get around this by offering benefits to athletes in hopes that they sign with them once they are done with college. Any contracts with an agent or benefits you have received from them will nullify your amateur status.
Agreement to be represented by an agent: As stated above, you are not allowed to sign any contracts to be represented by an agent.
Delayed initial full-time collegiate enrollment to participate in organized sports competition: The NCAA allows a 1-year grace period for enrollment after you graduate high school. After the one year period the NCAA may start taking away your eligibility. The NCAA allows you to have 5 seasons in which you can compete in 4. The fifth year is called a red-shirt year. A red-shirt year allows you to sit out a year of competition for various reasons, without losing one of your 4 years of competition.
Any financial assistance based on athletics or skills or participation: The NCAA does not allow you to benefit financially from your athletic skills or fame. This includes making money on autographs, free haircuts, and many other things. The National Association of Intercollegiate Athletics, or NAIA, allows only amateurs to compete in NAIA athletics. You will lose your amateur status for turning professional in a sport, but you will only lose amateur status in that sport.