PO and SM executing work in sprint backlog

The roles of SM & PO don't expect them to work on PBI, but having an individual endorsing several roles is not forbidden by the rules of the Scrum framework.

Be cautious with the disturbance it could create.

Scrum defines roles.  Roles can be fulfilled by many job titles.  For example, the role Development Team is most likely fulfilled by back-end engineers, UI engineers, quality engineers, etc. The intention isn't to have separate job descriptions for each role. It is to have the skills needed, the focus on the activities, and values associated to role present in the Scrum Team.

I have worked with teams where the Product Owner and Scrum Master also contributed to the engineering work.  But in all of those cases, there were struggles to adequately accomplish the roles of Product Owner and Scrum Master because of the split focus on the people doing dual roles. 

Short term assistance is not something I would discourage, but a long term committment to doing dual roles is not something I am willing to encourage.

Given this, can the SM or PO also work on ths items in the sprint backlog?

Yes. Whether they should is another matter, and something to be determined by a skilled team operating in its own context.

In other words Scrum is minimally prescriptive, and it would be overly prescriptive to say they couldn't.

I currently work with Development Teams that are exclusively made up of software engineers.

We sell our product to other businesses, and tend to maintain close personal contact with customers.

One thing I've observed recently as the Scrum Teams have started embracing outcome-oriented Sprint Goals is that the Product Owner plays a very direct role in communicating with customers, encouraging them to use what we've released, and provide the necessary feedback so that we can achieve our goal.

For now, I think we're all happy to see this as the responsibility of the Product Owner. After all, this ties in very strongly with product discovery and the decision to release. But it is arguable that this responsibility (and the associated skills) should belong in the Development Team.

Would it be better for us to have the Product Owner in the Development Team? I haven't seen enough evidence for that yet, but I'm curious to see what emerges with this approach. Collaboration is already at such a level that I think the only change in activity would be the Product Owner attending and contributing to the Daily Scrum.

"The Product Owner and Scrum Master roles are not included in this count unless they are also executing the work of the Sprint Backlog."

 

I've always interpreted this as Product Owner and Scrum Master are roles that can be combined with Developer roles, if there's no need for a full-time dedicated PO or SCM.

For example a full-timer that is part-time Product Owner and part-time Business Analyst or a full-timer that is part-time Scrum Masterr and part-time Test Analyst or Programmer.