How do I kick a player in an ongoing game?

As a Host of a party you can kick a player in a game pasting /kick in the chat and select the player you want to kick.

This feature is active for Live Challenge for now.

Please note that this will not ban a player from a Party lobby, if you wish to ban the player that can be done through the Lobby before or after a game by clicking on the player and press "Kick out".