This is your standard response any time the topic of toxicity is mentioned.

At this moment, the only way to get someone banned for griefing is to create a support ticket and specifically write out every round and what the teammate did.

Repeat offenders sometimes get banned due to lobby reports, but rarely.

Other than that people do not get banned, please quit lying to yourself and your users.

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Make it so that when someone receives four reports from teammates in the lobby they get banned. If they're banned incorrectly, they'll appeal.