Front-running in blockchain networks involves searcher bots scanning pending transactions in the mempool and submitting transactions with higher gas fees to prioritize their execution and capture profitable opportunities.

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During that window, bots can see every pending, unconfirmed transaction–essentially peering into the future and allowing them to front-run trades

One common scenario where MEV comes into play is in the context of decentralized exchanges (DEXs). Arbitrage opportunities, where a trader profits from price discrepancies between different markets, are built into the design of DEXs. Miners, aware of these opportunities, can sequence their blocks in such a way as to exploit these arbitrage opportunities before other traders, effectively 'front-running' them.

Some searchers will use bots called 'generalized front-runners' to scan the mempool for profitable transactions. Once a profitable opportunity is detected, the bot will replicate a user’s transaction with a higher gas price so that miners will choose that transaction over others

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Maximal Extractable Value (MEV)