Slashing

In proof of stake, validators lock up tokens as a security deposit. If they act in ways that could undermine consensus, the protocol confiscates part of that stake and ejects them. On Ethereum, the slashable offences are proposing two different blocks for the same slot and signing contradictory attestations, both forms of double voting that could support an attack.

Most slashing incidents come from operational mistakes rather than attacks, typically running the same validator keys on two machines at once as a backup. Penalties grow when many validators are slashed around the same time, so a correlated failure at a large operator costs more than an isolated one. Restaking protocols such as EigenLayer add further slashing conditions for services secured by restaked ETH.

Slashing is distinct from the smaller penalties for being offline. Stakers who delegate to a provider or use liquid staking share the loss if that operator is slashed, which is why operator diversity and track record matter.