The Black Lives Matter (BLM) hashtag is now a robust feature of the Twitter landscape. With millions of Twitter mentions since 2013, the Black Lives Matter hashtag eventually grew into a top 10 trending topic across 2015. While claims of origin are easily substantiated, the idea that user behavior on Twitter built this movement has not yet been closely investigated. Social sharing of emotion and gratification of self expression scholarship inform this research. Tweets from 2015 were used to identify the most prominent themes and names shared under the BLM hashtag. A grounded theoretical approach also investigates how tone and the presence of critics impacts the attitudes represented on Twitter. This case study aims to reveal what themes and events inspire Twitter users to generate content about racial justice. Measures of tone and analysis of how dominant attitudes can shift over time provide insights for future activists. In a content analysis of 1,001 tweets spanning an 11-month period, criticism was the third most prominent theme in the data set (15%). Regarding tone, only 65% of tweets using the BLM hashtag voiced support for the movement and levels of support fluctuated throughout the year. Opponents of BLM were most vocal during the month of August (27.5%) and shared the least during March (6.6%) of 2015. Keywords: Twitter, #Blacklivesmatter, grounded theory, social sharing of emotion, social media, user-generated content, gratification of self expression.