3. (a) That's right. The liability of a principal in tort law for the wrongful conduct of their agent who causes harm to a third party depends on the degree of control that the principal exercises over the way in which the agent carries out their work.
Generally, a principal is not liable in tort for the conduct of an agent who is an independent contractor, and who is therefore not subject to the principal's control in the way they carry out the work. By contrast, a principal is generally liable in tort for the conduct of their agent who is an employee and therefore subject to the principal's control. In the present case, B appears to be an employee rather than an independent contractor.
However, it must also be shown that the agent has caused harm while acting in the course of their employment. That is, the agent's conduct must have taken place while doing something they were authorised or instructed to do, or while engaging in activity that is incidental to something they have been authorised to do, even if they do it in an improper way, for example, negligently. In the present case, although B has acted improperly in forcing his way past the foreman, he does so while doing an authorised act (visiting a site to obtain an order). A will therefore most likely be vicariously liable for the harm.