Like Taz said a gut shot on a still deer usually produces a hunch up, blood will be small but should still be around in speck form, also you should find a greenish/bile tinge if you gut shot him. The leg kick is usually a vital hit indicator, however it is possible you grased him in the rear ham area which can produce a kick/slip response. Dark brown hair you found would most likely indicates a body hit of some sort. What position did you notice his head to be in when fleeing?(this can also indicate how hard he has been hit)
By the sounds of it, there is little doubt you put a hit on him and most likely he is down for good, I would head out with a couple of guys and comb the area. I have usually found a deer hit heads for the lowest, thickest stuff and then pile up if at all possible. Flat terrain they will usually head to some sort of heavy grass or terrain then bed down.