If we're playing in the woods with friends I highly doubt anyone here would play by such formal (and tourney) PSP rules. I agree with Party of A5, count it as a melee attack (but I do agree with NO PHYSICAL CONTACT). Another guy said "in battle you wouldn't throw a spent casing and kill someone", but you would take a knife to his side or big stick to his head
EDIT* Or YES, a grenade, good point DonkeyKnocker