This paper investigates the nature and role of controversial posts on Reddit by analyzing posts from four diverse subreddits: US politics, World politics, Relationships, and Soccer. It develops a classifier to predict the occurrence of controversial posts based on discussion thread features. The study finds that controversial posts are not typically due to trolling but often result from polarizing topics, off-topic content, or mentions of specific entities. Different subreddits exhibit varied behaviors, and key features influencing controversy are identified.