As of June 2018, California Interscholastic Federation has passed a law that allows for players to compete in 11v11 games as long as it is outside of their High School Team Construct.
This ruling is Bylaw 600F: Spontaneous Recreational Activity
It is permissible for a high school team member to participate in a spontaneous recreational activity or game in which sides or teams are chosen without regard to players representing any group or organization. Such participation would not cause loss of eligibility. (Definition of spontaneous: no prior planning or notice; an unplanned part of another activity which has a primary focus other than the sport.).
Q&A (DIRECTLY FROM CIF RULEBOOK)
Q: Is attendance by an individual student-athlete at a non-school practice, camp or clinic considered participation on an outside team if during that sport’s season of sport?
A: No. Individual student-athletes may attend a non-school practice, camp or clinic during that sport’s season of sport (unless your school and/or CIF Section has developed a more restrictive rule).
EXACT CAMP GAMES ARE ALLOWED DURING CIF SEASON
Mike Middlebrook (CIF) concurred clearly that 11v11 scrimmages in the context of EXACT events are completely permissible. However, if a team of players from the same CIF high school institution attends an EXACT camp, you must notify us so that we can split you onto different groups and avoid having you play as a team (as this would violate outside practice and competition policies).
SCREENSHOT FROM CIF BYLAW RULES:
Do you or your school's AD have further questions? Please have them reach out to us at firstname.lastname@example.org and we can clarify how the EXACT Camp is 100% permissible per CIF rules during the current high school season. You are allowed to attend camp.