战败 is a separable verb (离合词) with two opposite meanings — 'to be defeated' (intransitive, often followed by 了 or 于) and 'to defeat' (transitive, takes an object like 敌人). Because it's a resultative verb-complement structure (战 + 败), you can split the syllables to insert aspect markers or quantity complements: 战了三次败 ('fought and lost three times') or 战得过败 ('can defeat'). Pay attention to context to tell which meaning is intended.