Side balancing is an arena setting that penalizes a country for outnumbering another country by a wide margin. The standard setting for the Main Arenas, is for Side balancing to be enabled. One can check the balancer status by right-clicking on the clipboard map and selecting "country status". The side balancer consideres the amount of all players on the arena roster regardless of them being in flight.
The penalty is assessed by limiting plane, vehicle, and boat availability based on its ENY value. When a player is faced with an ENY limiting their plane or vehicle choice, they have the option of either staying with their current country and accepting the penalty. Or they may switch to the lower numbered country that is not ENY limited.
An ENY limit starts when a country has more than a 10% point advantage on the lowest numbered country. The ENY limit will raise by an approximate value of 1.59 for every percentage point advantage above 10%. The graph below also illustrates how the ENY limit raises in relation to the percentage point differences of the low numbered country and the other two countries.