One of the basic ideas in Scrum is the backbone formed by Product Owner and the Agile Team, headed by their Scrum Master.
The Product Owner stands right in the middle of the business, knows every functional detail, is trusted and respected by his business colleagues. Furthermore he takes care of the acceptance and business implementation of products and features delivered by the Agile team.
The Scrum Master, with his team, takes care of the technical realization and delivery of new products and features.

Scrum advocates a very short, direct connection between the one who has a goal and the ones who deliver the solution to reach this goal. Scrum does not know a Projectmanager role. Traditional projectmanagement responsibilities are divided over the Product Owner and the Scrum Master roles.

Product Owner and Scrum Master manage the work
In Scrum the traditional projectmanagement responsibilities are divided over the Product Owner and the Scrum Master roles.The Product Owner
• Owns the product backlog and while doing so, report on status of individual and clusters of user stories to stakeholders.
• Is responsible for the business case of every user story on his backlog. For every user story the potential value is estimated and this value is the base for prioritizing. The team will help by estimating the cost and is transparent in status and progress.
• Will perform stakeholder management to keep all stakeholders informed and take care all stakeholders interests are considered seriously.
• Chases impediments within his range of influence (policy / decisions needed, availability of business resources), until they are resolved.

The Scrum Master
• Will perform stakeholder management with respect to the delivery process. He will take care that all contributors are aligned, and that the team will deliver a complete solution, something the business really can use.
• Will assure the processes are in place to give full and honest insight in estimations, impediments, quality, progress and planning from a technical point of view.
• Chases impediments within his range of influence (technical environment, technical choices, availability of technical resources) until they are resolved.

When the going gets tougher
In non-complex environments and smaller changes this will work perfectly well: Product Owner and Scrum Master will be able to fulfill all project management tasks, and happily deliver valuable solutions in the same time. However if the environment becomes more complex, the Product Owner and Scrum Master are stretched in amount of effort and in competences requested.

Complexity and required effort to manage it rise when:
• Changes are bigger and more complex,
• The number of stakeholders grows,
• Stakeholders are more demanding,
• More and more distant parties are needed to realize a solution,
• The number of dependencies between teams and external parties grows,
• The business is more diverse, the number of business owners grows,
• The business implementation is larger in terms of number of people involved or in gap between current and new way of working.

There will be a moment the Product Owner and Scrum Master spend most of their time on all kind of ‘management’ tasks, instead of their main responsibility: delivering high quality user stories and solutions for the business. Mostly the latter is also the field their passion and qualities are in.
At this moment it is time to bring in someone with project management competences. To support the Product Owner and Scrum Master, with planning, managing external partners, reporting, communication and planning trainings for end-users. To pave the way for the teams.
This role is a major difference compared to the traditional project manager role. A project manager would take the lead and position himself as superior of the PO and the SM. The person we look for in an Scrum context is someone we is more like an assistant, although in practice I see him more like a peer, forming a team of three with the PO and SM to get the work done together.

Conclusion
In Scrum theory there is no room reserved for project managers. Together the Product Owner and Scrum Master will take care of all typical project management responsibilities. But in our daily complexity these project management activities can distract the Product Owners and Scrum Masters attention away from their primary responsibility and passion: delivering solutions. Bringing in support with project management competences can relieve our key-players and bring their focus back where it belongs. This support will act as a peer to the PO and SM, not as a manager.