A day after a 7.65% plunge, KOSDAQ's 5.27% rebound trips a buy-side sidecar

A 7.65% fall ^[5] takes an 8.28% rise to undo ^[12], so Friday's 5.27% ^[4] was never going to be a full repair. In points the picture is the same. Seoul Economic Daily put the previous close at 760.82 ^[5]; working back puts the close before the plunge near 823.8 ^[7] and the loss at about 63.0 points ^[8]. Yonhap News Agency had the index at 800.90 on Friday afternoon ^[4], a gain of about 40.1 points ^[9] and about 64% of the loss ^[10]. That is an afternoon reading, not a close.

We think thin liquidity is the likeliest explanation for a swing of this size, and we hold that loosely: it is a hypothesis the order book would have to confirm. Index levels and trigger rules measure volatility directly and liquidity only by inference. The counter-reading fits the same numbers. A market that regains 64% of a 7.65% loss in a session ^[10][5] may simply be one where buyers turned up once prices fell. The buy-side rule also asks for twice as much from KOSDAQ 150 futures (6%) as from the KOSDAQ 150 index (3%) ^[13][15], so a futures-led squeeze is a candidate explanation too.

The view fails if KOSDAQ closes above 800 on ordinary turnover, because that would make the swing a repair. It gains support if another sidecar or circuit breaker fires in the next few sessions, or if the index slides back toward the 760.82 close ^[5].