battle royal; large-scale free-for-all
Refers to a chaotic, large-scale fight involving many participants, often with no clear sides or rules. Used in sports, games, or metaphorical contexts.
The match turned into a huge free-for-all at the end, and the crowd was thrilled.
A battle royal broke out in the game, and it became impossible to tell friend from foe.
Compound of 大 (dai, 'big') + 乱戦 (ransen, 'chaotic battle'). The exact historical derivation is uncertain, but the word follows a common pattern of intensifying a noun with 大.