A nominal bears the instrumental role if it serves to express the instrument (implement carried in the hand, body part, means of transport, or language) with which an action is carried out by the agent.
instrument (SEM) = a semantic role including participant roles for a participant that is manipulated by the agent to bring about an event. Example: in Jack broke the window with a rock, the agent (Jack) manipulates the rock to bring about the breaking of the window. (Sections 6.1.2, 6.2.1)