“Restricted” means the play may be unavailable for you to produce. There are many possible reasons for this. There may be a West-End production, national tour, or nearby professional production running or in the works.
If the title is “restricted”, we still encourage you to apply as approvals are possible. We can never guarantee approval as restrictions constantly change; we suggest applications for a few titles so that you are not left without a show to fill that slot in your season.