godan verb (-su)
start acting violently; begin to rampage; grow restive
Describes the onset of violent, unruly, or rambunctious behavior. Often used for people, animals, or natural forces becoming uncontrollable.
酔っ払いが突然暴れ出した。
The drunk suddenly started acting violently.
嵐で海が暴れ出す。
The sea begins to rage in the storm.
Standard kanji spelling.
Variant with だす in kana; equally common in practice.
暴れる means 'to act violently' or 'to rampage' as a state or action, while 暴れ出す focuses on the beginning of that action.
Compound of 暴れる (abare, 'to act violently') + 出す (dasu, 'to start doing'). The 出す suffix indicates the beginning of an action.