Backrunning
An MEV strategy in which a bot places its own transaction immediately after a target transaction in the same block, to capture value created by it.
Backrunning is a maximal extractable value (MEV) strategy where a searcher or bot submits a transaction designed to execute immediately after — rather than before — a specific target transaction within the same block, aiming to profit from a price or state change that the target transaction itself causes. Because block builders (see Kaavon's "Builder (MEV)" glossary definition) typically have flexibility in how they order transactions within a block, searchers can bid for the exact slot immediately following their target.
Backrunning is distinguished from front-running (see Kaavon's "Front-Running" glossary definition), which places a transaction before the target to profit from anticipated impact, and from a sandwich attack (see Kaavon's "Sandwich Attack" glossary definition), which combines both a front-run and a backrun around the same target transaction. Backrunning on its own is often considered less harmful to the original trader than front-running or sandwiching, since it doesn't directly worsen the execution price of the target transaction — common examples include arbitraging a price imbalance a large trade just created, or liquidating a position that a preceding transaction just made eligible for liquidation.
Examples
- A backrunning bot might detect that a large swap has just pushed a token's price out of line across two exchanges, and immediately submit an arbitrage trade in the very next transaction slot.
- Backrunning a liquidation-triggering transaction lets a searcher be first in line to claim the liquidation bonus the moment a position becomes eligible.