The gaming industry is affected by two key issues—cheating and DDoS attacks against game servers. In this paper, we aim to present a novel yet concrete application of the blockchain technology to address the seemingly disparate problems. Our approach uses blockchain to manage definitive game state and exploits peer consensus on every player action to track modifications to tangible player assets. While a key impediment to adopting blockchain for real-time systems is its high per-operation latency, our approach leverages several optimizations to enable real-time prevention of a large class of cheats where the reported client state is inconsistent with the observed state at the server. Further, blockchain-based games leverage the robust peer-to-peer architecture to successfully defend against DDoS attacks. Our strategy enables flexibility to customize games with minimum modifications to game clients by porting server-side logic to smart contracts that execute atop peers. We evaluate our approach on a recent port of the multi-player game Doom. Our prototype can scale to client tickrates matched by modern games, and prevent cheats in <150ms for 32 peers deployed across the Internet, which is well within the latency requirements for online gaming.