User reviews published in mobile app repositories are essential for understanding user satisfaction and engagement within a specific market segment. Manual analysis of these reviews is impractical due to the large volume of available data, while automatic analysis poses several challenges, including data synthesis and effective reporting. These challenges complicate the task for app providers in identifying hidden patterns and significant events related to app acceptance, especially in assessing the influence of competitor apps. Furthermore, review-based analysis is mostly limited to a single app or a single app provider, excluding potential market and competition analysis. Following a case-study research method in the microblogging app market, we introduce an automatic, novel approach to support mobile app market analysis processes through quantitative metrics and event detection techniques based on newly published user reviews. Significant events are proactively identified and summarized by comparing metric deviations with historical baseline indicators within the lifecycle of a mobile app. Results from our case study show empirical evidence of the detection of relevant events within the selected market segment, including software- or release-based events, contextual events and the emergence of new competitors.