When a team loses the point for not being there when they absolutely could.
If they are forced off the point by some type of ability or just by being outnumbered then it's not a c9, if you call c9 when it's not a c9 then you're cursed to never get out of plat.
Cloud 9. They had one of the top teams in OW and they lost the finals by getting off point (if I remember correctly) so leaving the point and losing is basically "pulling a C9".
It originally was when cloud 9 could have won a game if they stayed on point, but lost because they stepped off. So you say c9 when a teamate can step on the point to contest in overtime but doesn't, causing a loss.
C9 is when a team 'abandons' or 'forgets' the point when they are preferably in the lead...and the enemy team takes the point 'under their noses'. Some people mistakingly call teams being FORCED to leave the point zoned out by (dva ult for example) and losing the match a 'C9'" Named after the team 'Cloud 9' who had this happen to them numerous times
Cloud 9 is a team. They left the capture point to get kills and lost because they were too busy fighting and forgot to contest. So now everyone clowns on then by saying C9