Community dynamics play an important role in the Open Source Software (OSS) development paradigm. Researchers have extensively studied the human aspects of the OSS paradigm from the point of view of community formation to community evolution. A few studies relate community dynamics with OSS product attributes such as code quality. However, the impact of community dynamics on non-code contributions such as commits has not been explored. In this paper, the aim is to analyze the impact of community dynamics on syntactic quality of commit messages of an OSS project. We first propose and validate a commit message quality model, and then use that model to analyze the OSS projects. Empirical analysis of seven OSS projects available in the Git repository shows that a small group of contributors active at the same time in a project leads to high syntactic quality contributions. These observations may prove useful to developers as well as project managers who need quantifiable techniques for monitoring the OSS projects.