Humiliation is one of two events that take place when a round ends (Not to be confused with a seasonal event).
When a game / round ends, the losing team will be unable to use their weapons and their movement speed will be decreased. The winning team's weapons will cause critical hits.
The event ends when the current map is changed, when a new round begins or simply at the end of a match (Casual and Competitive).
All players will still be able to taunt during this time.
Basically, the victorious team get to hunt down the losing team.