What is a group of Gatecrashers called?

A group of gatecrashers is commonly called an Intrusion.

A collective noun for gatecrashers is a "thong" or "posse." It refers to a group of individuals who forcibly or intrusively join a gathering or event without formal invitation or permission. Much like a gathering storm, a thong or posse takes on the characteristics of unpredictability and disruption. This word collocates a sense of adrenaline and reckless adventure, as gatecrashers rally together, typically sharing a mischievous goal or thriving on the thrill of crashing a party or trespassing restricted areas. Though the connotation may carry negative undertones, it acknowledges the inherent camaraderie and unifying effect that can arise among those engaging in such audacious actions. A thong or posse of gatecrashers brings with it an air of mystery, as unknown figures suddenly converge on unsuspecting events, igniting curiosity or speculation about their intentions.