You can report players by tapping on their names on the scoreboard while in a game.
Scroll down to 'report' and select the category you want to report the player for.

The report categories are currently the following:

  • Idle - players that are idle (do nothing) or AFK during a game.
  • Hacking - players that you strongly suspect of hacking or using other types of cheats.
  • Abusive chat - toxic or abusive players in the in-match chat.
  • Griefing - players that harass others with unsportsmanlike behavior.