Whether MEV is illegal, if we refer to the traditional financial practice of forward running trading (brokers profiting from customer order information), it is usually illegal. Therefore, in terms of characteristics, this is similar to sandwich attacks. However, in this special environment on the chain, it is still difficult to define because the memory pool is public and everyone can see it. In theory, this belongs to a first come, first served open competition, rather than exploiting information asymmetry. Moreover, not all MEVs are harmful, and some arbitrage and clearing transactions also maintain on chain stability. Therefore, in the future, it is estimated that regulatory definitions of toxic MEVs and benign MEVs will be needed.