A jab, whether in the sense of a punch or an injection, may be seen as an act of aggression. From a spiritual perspective we may need to ascertain what is causing that aggression.
Psychological / emotional perspective: By its nature a jab is a short sharp action, often containing an element of surprise. It will depend on other circumstances in the dream how this element of surprise is interpreted. We may need a short sharp shock to move us from our present emotional stasis.
Material aspects: Jabs are straight, arm-length punches thrown from the leading hand. In dreams we must decide whether the action is defensive or offensive before we interpret them in terms of what is occurring in everyday circumstances.
If the fight is structured as in a boxing match this action may refer to working difficulties.