There are three game modes in random battles (not clan battles): Standard Battle, Encounter Battle and Assault. Standard mode is available for everyone and it is impossible to turn it off.

Encounter battles are available to vehicles of tier 4 and higher.

Assault battles are available to vehicles of tier 6 and higher.

All these battle modes are designed to bring some variety in the game, but often do not change anything: sometimes defending team is attacking etc.

Standard game patterns for every map are published in the Maps section.