Optimistic concurrency control (OCC) is inefficient for high-contention workloads. When concurrent transactions conflict, an OCC system wastes CPU resources verifying transactions, only to abort them. This paper presents a new system, called Network Optimistic Concurrency Control (NOCC), which reduces load on storage servers by identifying transactions that will abort as early as possible, and aborting them before they reach the store. NOCC leverages recent advances in network data plane programmability to speculatively execute transaction verification logic directly in network devices. NOCC examines network traffic to observe and log transaction requests. If NOCC suspects that a transaction is likely to be aborted at the store, it aborts the transaction early by re-writing the packet header, and routing the packets back to the client. For high-contention workloads, NOCC improves transaction throughput, and reduces server load.