ASSISTING LEADMAN IN COUPLING TRAILER TO MAINENENE VAN. AFTER LOWERING HITCH ONTO BALL, EE PUT HIS FINGER BETWEEN BALL & HITCH TO CHECK CONNECTION.LEADMAN SHUT OFF VAN & TOOK HIS FOOT OFF BRA KE. THIS CAUSED A SLIGHT MOVEMENT OF HITCH & BALL. EE'S FINGER WAS PINCHED BETWEEN HITCH & BALL POOR COMMUNICATION & INATTENTION TO DETAIL OFTASK AT HAND CAUSED THIS ACCIDENT