The most infamous "VAC crowd" moment in the Dota 2 Manila Major 2016. This clip features the Filipino team Mineski against the Swedish team Alliance.

"VAC" is short for the Valve Anti-Cheat system and is used by the community to refer to moments in a Valve video game that could be considered cheating. "VAC crowd" refers to a biased crowd of any live tournament (of a Valve video game) that actively helps its favored team by providing crucial auditory hints through crowd noise. Both terms are used in the Twitch streaming platform. The effectiveness of a VAC crowd depends on how good the soundproofing is for the tournament.

In Dota 2, VAC crowds significantly increase the difficulty for the opposing team to perform successful ganks.

This clip is taken from the YouTube video "The Manila Major Main Event - Day 1 - Alliance vs Mineski (bo1)" by PGL, at around 1 hour and 4 minutes.