Quick Answer
A lock limit is when the price pins to the daily limit because the order imbalance is so one-sided that no counterparty will trade there. With remaining orders outside the limit, effectively no trading occurs, and a trader on the losing side is "locked in," unable to offset until the imbalance eases or the exchange expands the limit.
The last two sections mentioned a market becoming "locked." This is the one case where trading truly stops. The key point is that the stop is caused by the imbalance, not by the limit itself.
What a Locked Limit Is
A locked limit is a limit move with no counterparty: the price hits the boundary and cannot move, and no trades can be matched.
- Lock limit (locked limit, or limit-locked market): the price moves to the daily limit and stays pinned there because the order imbalance is so one-sided that there is no willing counterparty at a tradeable price. Effectively no trading occurs, because all remaining orders sit outside the daily limit.
- Why no trade matches: a market is "locked" when the bids or offers are outside the applicable daily price limit, so no trade can be matched within the allowed range. There is plenty of interest on one side and almost none on the other.
Think of it this way: imagine an auction where every hand in the room shoots up to buy at the highest allowed price, but not a single person is willing to sell at that price. The auctioneer is stuck. There is enormous demand, yet no sale can happen, because a trade needs both a buyer and a seller and one side has vanished. That stalemate at the boundary is a locked limit.
Exam Tip: Gotchas
- A locked market is caused by the imbalance, not by the limit. A contract can reach the limit and keep trading at it as long as willing buyers and sellers meet there. It only locks when one side has no counterparty. Do not describe every limit move as "locked."
The Two Lock Scenarios
Locking happens in both directions, and the trapped trader is different in each.
| Scenario | Order imbalance | Result |
|---|---|---|
| Locked limit up | Many buyers at the limit, essentially no sellers willing to trade at (or above) it | Price pinned at the upper limit; a short who wants to buy back (offset) cannot find a seller |
| Locked limit down | Many sellers at the limit, essentially no buyers willing to trade at (or below) it | Price pinned at the lower limit; a long who wants to sell (offset) cannot find a buyer |
Exam Tip: Gotchas
- Locked limit up traps the short; locked limit down traps the long. In a lock, the trader who needs to trade is the one facing a wall of same-side orders and no counterparty. A short trying to buy back cannot when everyone is buying (locked up); a long trying to sell cannot when everyone is selling (locked down).
Being "Locked In"
The practical consequence is a trader who cannot get out, which is why locking is the most dangerous scenario in the unit.
- Locked in: a trader on the losing side cannot get an offsetting trade filled, because no counterparty exists at the limit. They are stuck in the position while the market cannot move past the boundary.
- How relief comes: the position frees up only when the imbalance eases (a counterparty finally appears at the limit) or the exchange expands or removes the limit so the price can move to a level that clears the backed-up orders.
Think of it this way: being locked in is like standing at the only exit of a packed room while a crowd surges toward the same door. You cannot move until either the crush thins out (a counterparty appears) or someone opens a wider door (the exchange expands the limit). Until then, you wait, and any losses on the position keep running.
Exam Tip: Gotchas
- A locked-in trader is stuck until the imbalance clears or the limit expands. Meeting a margin call does not unlock the market; it only keeps the account funded. The position itself cannot be closed until a counterparty appears at the limit or the exchange widens or removes the boundary.