How does the Scrum Framework work without a Project Manager?
In a traditional project normally a product manager defines the requirements. Realization is then delegated to a project manager and he coordinates all activities needed to realize the project.
The Scrum Framework does not define a “project manager” in the classical sense although these activities are of course required. Within the Scrum Framework the responsibilities of a project manager are distributed over the roles of the Scrum Product Owner and the Scrum Master.
The definition of the role and responsibilities of the Scrum Master takes into account that decisions about functionality, release plan and costs can done much easier and better if one person is responsible for the content and the planning. Otherwise there will always be a tension between the Scrum Product Owner (not responsible for the project) and the project manager (not responsible for the content). If these responsibilities are combined everything will be much easier.
Nevertheless the Scrum Master will take over some of the responsibilities of a traditional project manager. Tracking the tasks within a Sprint and resolving impediments are within his responsibility. Since he is part of the Scrum Team it is much easier and much more efficient to handle such topics directly in the team.