Does the following sound sufficient?—
- While a contest is underway, no one other than a contest admin can see the scores and participants.
- Everyone can always (even without logging in) see the basic details of all contests (name, dates, included index pages, and admins' usernames).
- After a contest is finished, everyone can see everything.
- Anyone can create a contest (after logging in) and in doing so become an admin.
- No one other than a contest admin can edit a contest.