This is what I have found out by reading the SCHSL Handbook's Constitution section.
SCHSL ConstitutionSeventh, Eighth and Ninth Grade Activities Rules and RegulationsThese regulations apply to all 7th, 8th and 9th grade students participating in Junior High or Middle School programs as well as students participating on exclusively 7th and 8th grade teams under the High School Program. All ninth grade students participating in a high school program will not be restricted by these regulations or the regulations restricting junior high school teams in the National Federation rules books.
Students below the seventh grade may not participate in interscholastic athletics. Students in grades 7 and 8 will not be permitted to participate on varsity interscholastic teams in football, wrestling, and soccer.
A-25 (bottom of page)A junior high or middle school student promoted to a high school varsity, junior varsity, or other interschool squad, may not return to junior high or middle school competition during the current year in the same sport if he has participated in a gmae played by the advanced squad.
A-27 (Soccer section)1. Practice may begin on January 26.
2. The soccer season will open on March 1 and close on April 17. Eligibility forms are due in the League Office at least 7 days before the first match.
3. Schools are limited to 12 matches.
4. A student will be restricted to one game per day except they may play in two games in one day in an invitational tournament. There must be a minimum of one hour's rest between games.