I've seen a lot of information on how to handle unplanned work, like adding in a buffer to each sprint to account of work that may come up that is not in the sprint backlog. However, I have come to understand that any interruptions that are acted upon during a sprint are not in fact following Scrum.
So to ensure that the essence of Scrum is alive and well in a team, does that mean that ultimately they should refuse any outside work on only stick to items in the sprint backlog. Especially if that outside work has nothing to do with their product?
TL;DR Send everyone to the PO, PO evaluates, conversations ensue, action is decided.
Anyone approaching your team with outside work should be directed to the Product Owner. From the Scrum Guide:
The Product Owner is responsible for maximizing the value of the product resulting from work of the Development Team.
How that happen is unique to each organization. But in all I have worked by directing people to the PO, there is one focal point. The PO will weigh the request against everything else in the Product Backlog and Sprint Backlog. If the PO feels that the current Sprint Backlog outweighs the new request, it goes to the Product Backlog and is ordered appropriately. If they feel it is important enough that it needs immediate attention, then a conversation ensues between the PO and the Dev Team. If the Dev Team feels that they can pull it into the current sprint and complete the work without jeopardizing the Sprint Goal, it happens. If they feel like it could endanger the Sprint Goal, it will be put in Product Backlog and ordered higher. If they feel it would require a swap of a story and that swap would not endanger the Sprint Goal, then that swap is done. But all of this happens with the Scrum Team present. We usually do it immediately following a Daily Scrum.
Each occurrence is considered unique and handled as such.
I have come to understand that any interruptions that are acted upon during a sprint are not in fact following Scrum.
Suppose a team framed a Sprint forecast and committed to a Sprint Goal. Part way through the Sprint an interruption happened which, if they acted upon it, would still allow their commitment to be met with some replanning. Do you believe this accommodation would be contrary to the rules of Scrum?
I would support what Daniel has said. Scrum/Agile encourages responding to change rather than following a plan.
Of course the responding to change element has to be balanced with current work at hand in terms of value added (via PO) and any trade offs well understood and transparent to stakeholders involved.
However when you say "Especially if that outside work has nothing to do with their product?", does this mean work completely unrelated to sprint team's focus is being asked of them? If this is something that would never even be a candidate for the product backlog that the team works on such as consultancy requests for another product, I would take a practical call depending on situation and if does not endanger sprint goal.
So, is it safe to assume that, when in doubt about unplanned work/interruptions related or unrelated to the product, allow the PO to make the decision? Since the PO is counting on delivering business value and that delivery is dependent on achieving the sprint goal, any activity that could distract the development team from the sprint goal should go through the PO? Depending on the frequency and nature of the interruption may be the PO can work with the Scrum Master to remove that interruption or leadership to find alternate ways to handle the interruption?
And I am assuming the reason to go through the PO, is to allow the PO to review the unplanned work/interruption and decide if there is benefit (business value) in adding to PB or adjust sprint goal.
Besides the Development Team to tell the PO about the unplanned work, they should also have courage to reject those unplanned work as they need to focus on the work in current Sprint to achieve the Sprint goal.