Blocking persons (for instance for sending you materials that in G+ would be a T.O.S. violation) is only possible by blocking them, not by reporting them.
Most hangouts users however do have a G+ account, so you can request a block there.
Relevant links:
- [Archive.is] hangouts.google.com
- [Archive.is] Block or ignore someone – Computer – Hangouts Help
If you don’t feel comfortable in a Hangout with someone, you can block them. When you block someone, they can see that you’re online but can’t send you Hangouts messages.
Tip: If you are contacted by strangers or spammers, choose who can contact you directly.
- [Archive.is] Manage your contacts – Computer – Hangouts Help
You can see your conversations, invites and contacts. Contacts that are online are at the top of the list with a green circle on their photo.
…
Let people contact you without an invite.
- [Archive.is] How do I report spam / nuisance hangout requests? – Google Product Forums
- [Archive.is] Report abuse on Google+ – Computer – Google+ Help
If you see something on Google+ that violates our User Conduct and Content Policies, you can report it. Violations might include: Bullying, threatening, or harassing someone Hate speech …
–jeroen
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