All attacking troops only have so much stamina before they will be forced to retreat. Normally, Troops will have 20 rounds of stamina in combat before they retreat. When an attacking troop runs out of stamina they immediately retreat from battle.
Losing Stamina[]
Destroying most Buildings will cause an attacking troop to lose 5 rounds of stamina. The exceptions to this are Towers , Cannon Towers, and Training Grounds that are below level 5.
Stamina in Strongholds[]
While attacking the gates of a stronghold , troops have 20 rounds of stamina as normal. However, once the gate falls and the troop battle begins, attacking troops can be in battle for any number of rounds until one side of the battle runs out of morale or is killed entirely.