Real-time multiplayer games are a popular application of networks, and as IEEE 802.11 wireless networks are widely used, games are expected to be widely played on wireless networks. However, 802.11 networks with the normal MAC (DCF) may present some challenges when supporting real-time games traffic. In this work, we present a theoretical model which can predict the performance and capacity of 802.11 WLAN for Quake 4, a real-time FPS game. Using the wireless network game model, we derive throughput, delay, jitter and MOS (mean opinion score) as the number of game clients increases in the WLAN and predict that the capacity of a default 802.11b wireless network can support around 10 players for Quake 4. In 802.11e networks, QoS (quality of service) is provided with 4 configurable MAC layer parameters. With the network game model, we show that with proper TXOP configuration at the AP and game server, the network can be optimized and its capacity improves to around 15 players.