Despite the growing interest in social media and user-generated content, both academics and practitioners are struggling to understand the value and consequences of social media (e.g., blogs). This study employed a 2 (media source: mainstream/ social media) × 2 (message valence: positive/negative) × 2 (team identification: high/low) between-subjects design on source credibility and attitude toward an article. Positive and negative messages about the university’s varsity men’s basketball team were presented in either the mainstream media (sport magazine) or a user-generated format (blog). The results revealed that message valence had a significant main impact on triggering biased source evaluation and attitude toward the message. In turn, media source had a significant main effect on source expertise, but no main effects were found for trustworthiness and attitude. Team identification moderated the effect of media source on cognitive processing, suggesting that highly identified fans evaluated mainstream content more favorably, whereas less identified fans preferred user-generated content.