Spot-futures arbitrage
Buying the asset on spot and shorting its futures contract to collect the basis, with no directional exposure.
When a perpetual or dated future trades above spot, you can buy the coin on the spot market and short the same notional in futures. Price moves cancel; what remains is the basis, plus any funding the short leg collects while the premium lasts.
The two legs can live on one exchange or on two. One exchange is simpler and often shares margin between the accounts; two exchanges widen the set of opportunities but mean the spot leg cannot backstop the futures margin without a transfer.
The main operational risk is the short leg's margin during a rally: the spot profit is real but not immediately postable as collateral. Withdrawal suspensions matter too — a spot leg you cannot move is a leg you cannot unwind on the venue that needs it.