[Rain Man]

I think guru's best hope is to hide, throw the rocks in a way that will make yhf look toward them, and then guru can spear him in the back. Other than that, he could be in trouble.

However, I should note that in Revenge of the Jedi, the ewoks used spears and rocks to take out a whole division of Imperial troops, so victory is indeed not only possible, but on record as having happened.