Acting in your Holacracy Coach role, address/"coach" the Lead Link who made the assignment to the ineligible party to abide by policies regarding eligibility. If the Lead Link doesn't see anything wrong with their assignment, you have authority in your Secretary role to communicate your interpretation of the policy (maybe reiterating the importance of why it was created in the first place). 

The situation is the result of either of the following:

• LL has a different interpretation of the policy or the situation, and argues that he's not violating the policy
  • In this case, clarify the policy and/or get a Secretary interpretation if you can't wait for the governance meeting
• LL isn't aware that s/he violating the policy
  • In this case, let him/her know
• LL is willfully violating the policy, which may be Individual Action:
  • If the LL is consciously taking IA, you can ask him/her to take a project to restore the situation, which would involve proposing a change to the policy.
  • If s/he's just violating the policy because s/he doesn't like it and is not taking IA, then it's trickier and should be treated like you would anyone else in the organization violating the rules (note it's not only an issue with Holacracy, it's an issue with any management system). It's a tension to process
    • I'd first try to talk to the LL and convince him/her to do the right thing
    • You could talk to the LL of the broader circle to consider removing him/her from the sub-circle LL role
    • You could propose some governance around what happens when someone's violating the rules, or trigger any existing process if there is already one in place 

Wow Olivier, so clear, thank you!!

Thanks very much for the responses, this helps quite a lot!