This study applies Activity Theory to describe and analyze an out-of-school project in which eight Chinese university students utilized a massively multiplayer online game (MMOG) to learn English. Based on data collected through questionnaires, gaming journals, gaming recordings and interviews, thematic analysis was performed to identify the recurrent themes, which were then mapped onto the activity system. Four contradictions were identified in the process. Temporary contradictions dominated the early phase of the project and were easily resolved. However, inherent contradictions, mainly manifesting themselves through inadequate competence and learner variation, remained unresolved. Efforts to overcome these tensions resulted in the evolvement of the activity system. In terms of the actual outcomes, there was evidence for the development and exercise of autonomy. Learners also reported enhanced confidence and gains in vocabulary, listening and oral fluency. The study contributes new knowledge to the field by revealing how non-gamers make use of digital gaming for language learning in an informal setting. Pedagogical implications for digital game-based language learning are discussed and suggestions for future research are also provided.