Are you required to call a judge if you're not involved in the game?
Covered by the Tournament Rules:


  Any person physically present at a tournament and not in any other category above is a spectator. Spectators are responsible for remaining silent and passive during matches and other official tournament sections in which players are also required to be silent. If spectators believe they have observed a rules or policy violation, they are encouraged to alert a judge as soon as possible. At Regular or Competitive REL, spectators are permitted to ask the players to pause the match while they alert a judge. At Professional REL, spectators must not interfere with the match directly.


(Emphasis mine)