The phrase crowded long is used loosely. It often means little more than a coin has rallied and the speaker is nervous. The word can be made precise, and the precise version is more useful.
Every long has a short
A perpetual contract has two sides. For each contract held long, one is held short. Open interest counts those pairs. So the long side is never larger than the short side in contracts. A market cannot be crowded in the sense of holding more longs than shorts. Ratios that seem to say otherwise are counting accounts or a subset of traders, which is why the long/short ratio needs care.
Three things that make a crowd
First, one side is paying. When funding is well above its resting value, longs are paying shorts to keep their positions. That is a published price for wanting to be long, as in funding as a crowding gauge. Second, that side is leveraged, so it has liquidation prices and cannot simply sit through a large move. Third, its positions were opened at similar levels, so its exits and liquidations cluster. A crowd is a group that would have to leave through the same door at the same time.
Who is on the other side
If longs are a crowd, the shorts are usually a different kind of trader. Many are market makers. Others hold the coin in spot and short the perp against it to collect funding, the trade described in the cash and carry trade. They are not betting on a fall. They are hedged, and a rally does not force them out. So one side can be crowded while the other is calm.
Crowded is not wrong
A crowded trade can keep working. Funding can stay high for weeks while price rises, and the crowd is paid in price for what it pays in funding. Crowding describes cost and fragility. The cost is the funding bill, which grows with time. The fragility is what happens if price turns and the cluster of liquidation prices comes into range.
How a crowd ends
There are two ways. The slow way is cost. Funding eats at the position until holders trim, open interest drifts down and the rate eases. The fast way is price. A move reaches the liquidation cluster and the venue closes positions by force, which is the sequence in liquidation cascades. Neither comes with a schedule.
Where to see it
The NoVo Crypto Market Map shows funding per venue, never blended, beside open interest and 24-hour liquidation flow. Those are the three ingredients, per coin and per venue. Dr. NoVo, a markets SI, reads whether they line up.