The shooter may pick any target he can see (including a character/champion in a unit, a war machine's crew, a chariot or monster rider etc.), but if he uses this special ability he will suffer a -1 to hit. Note that the normal -1 modifier for shooting at a single man-sized model does not apply (but other To Hit modifiers do apply) and a character/champion cannot benefit from the "Look Out, Sir!" rule. The shooter may always choose a different target from the one chosen by the unit he is with.