A cross-functional Scrum Team holds all the skills necessary to create value each Sprint. The practical test is whether the team can take an item from the Product Backlog and reach the Definition of Done without waiting on anybody outside it.
The wording repays a slow reading. The Guide does not say the team holds every skill anyone might ask of it, and the phrase it uses is the skills necessary to create value each Sprint. That phrase sets the size of the skill set, which is whatever carrying one item all the way to Done inside a single Sprint requires.
Cross-functionality is a property of the team
Cross-functionality belongs to the team, so no single person has to hold every skill. People keep their specialisms, and a team of five who each know a little about everything and nothing deeply is usually worse at building a product than a team with real depth in it. The requirement is that no skill needed to finish a Sprint's work sits outside the team.
A database specialist is not a problem on their own. The problem appears when that specialist is the only possible route to any change in the schema, because the rest of the team stops whenever that person is away. Depth is worth keeping, and a single point of failure is worth removing.
Why an outside dependency breaks the Sprint
A single point of failure inside the team is one problem, and a skill that sits outside the team altogether is a larger one. Work that needs a team outside the Scrum Team cannot be finished on the Scrum Team's own decision. It finishes when the other group reaches it, and that group is ordering its own queue against its own priorities. A Sprint is a fixed length container for producing at least one usable Increment, so work that leaves the container to wait in somebody else's queue reliably comes back after the Sprint has closed.
The cost goes beyond a late item. Scrum runs on inspecting a real Increment and adapting from what is learned, so a dependency that defers completion defers the feedback by the same amount, and the team ends the Sprint holding work nobody can inspect.
How cross-functionality connects to the Definition of Done
If the Definition of Done includes a security review and a load test, the team needs both skills, because neither criterion can be met inside a Sprint without them. A Definition of Done a team cannot satisfy on its own is a signal that either the team composition or the Definition has to change.
The two options are not equally good. Loosening the Definition to match the skills a team happens to have produces an Increment that is not usable, which is the worse of the two outcomes. If the organisation has set a standard, a Scrum Team may apply stricter criteria and never looser ones, so the honest route is to bring the missing skill inside the team.
Broadening the skills the team already has
If a gap exists, the instinct is to ask for another person. Hiring is slow, it is often refused and it adds one more person whose absence stops the work. The route that holds more often is to broaden the skills already present and to remove the handoffs that made the gap visible.
Broadening skills means three habits in practice.
- Whoever holds a skill teaches it, and stops performing it on request.
- Two people pair on work that only one of them can currently do.
- An approval step outside the team gets challenged as an impediment, since some of those steps turn out to be a policy nobody has reviewed in years.
The Scrum Master coaches the team in cross-functionality and causes the removal of whatever keeps a gap in place, and that work usually sits outside the team.
The Scrum Master's part in closing a skill gap
Coaching and causing the removal are the two verbs the Guide uses here, and neither of them means doing the work. Coaching the team members in self-management and cross-functionality is one of the four services owed to the Scrum Team. The Scrum Master helps the team name the skill it is missing and argues with the approval step that keeps the gap in place, and the question of who learns what stays with the team.
The failure worth naming is a Scrum Master who closes the gap personally. Writing the missing tests or running the release by hand gets the Sprint finished, and it removes the pressure that would have grown the skill. The team therefore stays dependent, and the dependency now rests on the one person whose accountability is the team's effectiveness. Doing the work also hides the gap from the managers who could pay to close it.
What the Guide does not prescribe
None of this tells a team how to be composed, because Scrum states the outcome and leaves the composition open. The Guide names no roles inside the Developers, asks for no skills matrix and sets no ratio of specialists to generalists, because the answer depends on the product and on what its Definition of Done demands. The one thing the Guide fixes is that every skill the Sprint needs sits inside the team.