Futures-futures arbitrage
Long the perpetual on the cheaper exchange, short it on the dearer one, and close when the two prices meet.
The most common cross-exchange route: the same perpetual contract is priced independently by every venue that lists it, so two of them disagreeing is a matter of when, not if. You take the cheap side long and the expensive side short in equal notional.
Both legs are futures, so neither requires moving coins — only margin on each venue. That makes this the fastest strategy to enter and exit, and the reason it dominates the table on volatile days.
Convergence is not guaranteed on a schedule. Two perps can stay apart for as long as the imbalance that created the gap persists, and each mark price is anchored to a different index. Sizing for the time the position may need to stay open matters as much as the entry spread.