There is a subset of users who seem to join as many Clubs as they can, which results in many/most public Club leaderboards being cluttered with activity by people with no real relationship to the club (e.g. a regional/city-oriented Club whose leaderboard is always dominated by activity from other countries).
For example, the user currently topping the neighborhood running group I was just looking at is a member of around 575 Clubs and records activity exclusively in a different state. I am not sure why these users do this, but it degrades the overall Clubs experience for everyone.
Clubs should not have to be made Private to avoid this, as that places an undue moderation burden on the Club admins and discourages organic community growth. There needs to be a middle ground for Clubs that are in between the small, tightly-managed Private groups of real-life friends on one end, versus national & worldwide "free-for-all" public Clubs on the other.
It would help reduce the impact of these "club spammers" if Strava were to cap the number of public, leaderboard-enabled Clubs each user is allowed to join, and retroactively remove users from all but that number of Clubs if they are already over the limit.
Users could still be free to join as many Private & partner/brand-oriented Public Clubs as they want.