It's on Arsenal p.17. Two interpretations here:
a) A troll picks up a human by his foot and wields him like a chain. This I think wouldn't use Unarmed Combat, as the table suggests...
or is it
b) the attacker tackles/rams/hustle/bumps into the defender with all his weight?
this leads to a few more or less stupid follow-up questions:
c) can I enchant a (dead) body for a weapon focus?
d) For the sake of using Adept Powers like Killing Hands/Distance Strike/Elemental Strike is this the same discussion as with Hardliner gloves, because using the Unarmed Combat skill doesn't neccessarily mean I'm doing unarmed combat?
e) In case said attacker has his speed augmented (e.g. Movement power), would it be reasonable to adjust the DV according to the Ramming Damage Table SR4A p169