What policies and tools help curb coordinated harassment on tabletop forums?

[JohnL]

I'm a moderator for a mid-sized forum about tabletop gaming, and we have a recurring problem where a small group of users targets others with subtle but persistent online harassment, like dogpiling on opinions, mocking playstyles in supposedly 'fun' ways, and sending aggressive private messages. Our current rules against personal attacks aren't catching this coordinated, low-grade toxicity, and it's driving away good members. How have other communities successfully updated their policies and moderation tools to address this kind of insidious behavior, and what's the best way to document patterns of harassment for potential bans without getting bogged down in 'he said, she said' drama?