When developers want to contribute to an open-source project, they fork the repository, make changes, and send a pull request to the core team to incorporate these changes back into the repository. However, some projects enforce this collaboration model even for changes made by core team developers. This potentially enhances the quality of the repository by adding an inspection step before accepting a contribution into the repository. In this context, though less frequently, the contributions may be rejected. The understanding of the factors that lead to the rejection of these internal contributions is crucial for the improvement of the ways core developers collaborate, having a direct impact on the team productivity. In this work we extract association rules from pull request data stored in software repositories in order to find factors that have influence over the decision of rejecting contributions made by core developers. In addition, we present a qualitative analysis of some cases, helping to understand the patterns that arose from the association rules. The results indicate that some key factors increase the changes of having internal contributions rejected: (i) the inexperience with pull requests; (ii) the complexity of contributions, as well as the locality of the artifacts that have been modified; and (iii) the contribution policy of the projects.
