Front-Running

Front-running is placing your own order ahead of a transaction you already know is coming, so you profit from the price move that transaction will cause. On public blockchains this needs no insider access: pending transactions sit in the mempool where anyone can read them, and a bot can submit a competing transaction with a higher fee to be ordered first. Block builders and searchers make this systematic, which is why it is discussed as a category of maximal extractable value rather than an occasional abuse. Users reduce their exposure by setting tight slippage limits, splitting large swaps, or routing through private transaction relays that keep an order out of the public mempool until it is included.