Many English as a foreign language (EFL) learners worldwide spend hours playing commercial-off-the-shelf massively multiplayer online games. They engage in a multitude of different interactions with the game environment and possibly with other gamers, using English as the predominant medium of communication. This raises the question of whether playing such games improves these learners'/gamers' speaking performance over time. Drawing on usage-based theories of language learning, this longitudinal mixed-methods case study addressed this question by measuring six EFL gamers' speaking performance in terms of complexity, accuracy, and fluency (CAF) over the course of six months, and exploring their perceptions relating to the gaming environment and their language learning. The participants played in two teams: Team 1 with low-intermediate and Team 2 with high-intermediate proficiency. Each team comprised three EFL gamers and a native English speaker. Overall, the results appeared positive for the EFL gamers on both teams but in different ways. Their speaking performance showed improvements in 50% of the CAF indices. These results are discussed in light of the gamers' perceptions about the dynamics of in-game communication, the game's socio-affective environment, and the development of their speaking performance.