The current blockchains do not provide any security guarantees to the smart contracts and their uses. In the spirit of decentralization and censorship resistance, they follow the paradigm of including valid transactions in blocks without any further scrutiny. Rollups are a special kind of blockchains whose primary purpose is to scale the transaction throughput. Many of the existing rollups operate through a centrally operated sequencing protocol. In paper, we introduce the Sequencer Level Security (SLS) protocol, an enhancement to the sequencing protocols based on the OP stack and Optimism Bedrock. This pioneering contribution explores the concept of the sequencer’s capability to identify and temporarily quarantine malicious transactions instead of including them in blocks immediately. We describe the mechanics of the protocol for both the transactions submitted to the rollup mempool, as well as transactions deposited from L1. We comment on topics such as trust and decentralization, and consider the security impact on the protocol itself. We consider implementation details using the OP stack and Geth. The SLS protocol described can be easily generalized to settings other than the OP stack, and can be used for purposes other than security.