Halk, fighting the effects of the bat's milk and his own natural rage at annoying invisible magical wibbly wobbly things, decided to imbue the rock with a little extra spin for good luck.
In so doing he managed, infact, to coin a new toss - the "Barbarian Ricochet Death Toss" although the secrets are available to only a chosen few who can decipher the mad ramblings of the barbarian who himself suffered severe concussion attempting it.
With a complicated wrist motion and strange dance like steps the barbarian leapt backwards, and worked himself into a frenzy, charged forwards and releasing the rock at the perfect angle to skim the magic of the party blocker. It proceeded to act against the laws of the conservation of energy by picking up speed with every bounce, until the brown blur became invisible to the eye.
Luckily, Halk was only skiffed by the returning projctile and so when the party was found he was able to be rescued.
Unfortunately the blow and the horror of the carnage behind him means that he isn't in a fit state to continue onwards. And really, if you can put together the pieces of the rest of the party then you are probably the sort of person who can do those double sided 1000 piece bean puzzles with their eyes closed, and not the sort of person who should be allowed near a computer.