On a successful throw, grenades land at the feet of the target they were thrown at. On an unsuccessful throw, grenades can land anywhere, at the GM's discretion, but are likely to be close enough to damage the intended enemy anyway.
Either way, grenades "go off" and deal damage to everything within their blast radius on the next Combat Turn of the character who threw them. In the intervening turns, a particularly brave character near the grenade can use a Move Action to make a successful Hard Speed Check to pick up the grenade. If the character succeeds, he can make aThrowing Weapons Test to throw the grenade elsewhere. If the character fails at picking up the grenade, he is right at ground zero when the grenade goes off.