Front-Running
Placing a transaction ahead of a known pending one to profit from its expected price effect.
Front-running means acting on knowledge of a pending transaction before it executes. On transparent blockchains, everyone’s pending trades sit visibly in the mempool, so bots can spot a large buy and rush their own buy in front of it — paying a higher gas fee to be ordered first — then sell into the price bump the original trade creates.
It’s a core category of MEV and a direct consequence of public mempools plus fee-based ordering. Mitigations reshape infrastructure: private transaction relays that hide trades until inclusion, batch auctions that remove ordering advantage, and encrypted mempools. Front-running is what makes “who orders transactions” one of crypto’s most valuable questions.