A student-athlete is a participant in an organized competitive sport sponsored by the educational institution in which he or she is enrolled.
Student-athletes must typically balance the roles of being a full-time student and a full-time athlete. Due to educational institutions being colleges, they offer athletic scholarships in various sports.
Many student-athletes are compensated with scholarships to attend these institutions but these scholarships are not mandatory to be considered a student-athlete.
In the United States, athletic scholarships are largely regulated by either the National Association of Intercollegiate Athletics (NAIA) or the National Collegiate Athletic Association (NCAA), which sets minimum standards for both the individuals awarded the scholarships (in terms of GPAs and standardized test scores) and for the institutions granting them (in terms of the form and value of the scholarships and the proportion of recipients who must ultimately earn degrees).
You must register with NCAA if you want to become a student-athlete. NAIA Guide