In the context of the Disciplined Agile (DA) framework, a 'specialist' on a Disciplined Agile Delivery Team is someone with a specific, specialized skill set or domain expertise that contributes to the overall development and delivery process. While the DA framework promotes cross-functional team members, it acknowledges that certain roles require specialized knowledge.

A Business Analyst (BA) is considered a specialist role because they bring specific expertise in requirements gathering, process analysis, stakeholder communication, and translating business needs into actionable tasks for the development team. According to PMI's Disciplined Agile guidelines, BAs provide value by ensuring that the requirements are well-understood and clearly defined, which is crucial in aligning the team's efforts with stakeholder needs.

On the other hand, the roles of Product Owner (B) and Project Manager (C) are more related to leadership, decision-making, and coordination, rather than specialized technical or analytical expertise. Stakeholders (D) are external to the delivery team and are not considered specialists within the team itself.