It depends on the state-- and state charter laws-- and to a lesser extent upon where the charter is actually housed. If it's housed within a home district, then there is a motivation to have an enrollment cap (so that the district can't gut other public schools by pulling enrollment $$ from struggling districts, especially rural/poor performing ones).
State charter enrollment laws will then dictate whether there is a waiting list at that point, or a lottery, or just what happens when there are more applicants than openings.
