This is the rule of the eligibility of option enrollment students.
Students who complete transfer requirements on or before March 15 and whose names are submitted to the NSAA by March 15 as transfer students shall be eligible immediately in the fall at the school to which they transfer. If the student were to later change his/her mind and not transfer, that student would be ineligible for 90 school days at the school in which he/she attends.
If the student were to transfer to the new school, but later decides to return to his/her former district before 90 school days have elapsed, such student will be ineligible in the former district for 90 school days, with the ineligibility period commencing at the start of the fall semester.
This rule does not affect freshmen. Their eligibility is established at the school they attend the first day of their freshmen year.