What does the cryptic crossword clue "Bit of a bar fight? It'll play out noisily, unless you keep the lid on it (5,3)" mean?

The wordplay uses a charade (building blocks). MUSIC (synonym="MUSIC") + BOX (synonym="BOX") = MUSICBOX The answer is MUSICBOX.

Bit of a bar fight? It'll play out noisily, unless you keep the lid on it (5,3)

Guardian Cryptic #27904 | 16 Down | 2019-08-20 flower