I don't know if it's still true, but players used to take classes in summer school so they could have a lighter schedule during the fall semester.
Here's a high-level overview of the current requirements.
I suspect that most football players only enroll for 12 credits in the Fall semester. Likely true for hoops in the Spring semester as well.
NCAA Academic Eligibility Standards
FULL TIME ENROLLMENT
To be eligible to participate in organized practice sessions, compete, and receive an athletics scholarship a student-athlete must be enrolled in at least 12 units.
NCAA Academic Eligibility Standards
FULL TIME ENROLLMENT
To be eligible to participate in organized practice sessions, compete, and receive an athletics scholarship a student-athlete must be enrolled in at least 12 units. (If participating as a graduate student, the individual must be enrolled in a minimum of 9 units.) While remedial credit may satisfy enrollment requirements, student-athletes must be aware that these units do not count as credit towards degree (except for up to 6 units during his/her freshman year). Transfer student-athletes who are required to take English 99 and/or Math 40 must enroll in at least 15 units.
CREDIT HOUR REQUIREMENT
Each year, all student-athletes must earn at least 18 units that count toward degree progress during the fall and spring semesters combined. Intercession units may also be used to meet this requirement, while summer units cannot.
SUMMER CREDIT HOURS
Six summer credit hours may be used to satisfy the 24-credit-hour requirement when certifying a student-athlete entering his or her second year of collegiate enrollment.
