This question applies to either OSRIC or to AD&D 1st Ed.
The scenario:
A human fighter with strength of 17 has selected "grenade-like weapons" as one of his weapon proficiencies. He carries a small bag with half a dozen mostly spherical baseball sized rocks for throwing at enemies.
He throws a rock at an ogre and scores a hit (not a critical hit or anything, just a normal hit).
How should the damage be calculated?
Best Answer
If you don't mind befouling your Advanced Dungeons & Dragons campaign with rules from that upstart impostor Advanced Dungeons & Dragons, 2nd Edition, the supplement Player's Option: Combat & Tactics (1995) has on its (extensive) Master Weapon List an entry for the typical, everyday can-be-thrown-by-a-normal-human rock (132).
(Note to New Readers: Just to be clear that this suggestion isn't overreaching, unlike later editions that change the game substantially, the differences between AD&D and 2nd Edition are far smaller, and a great deal of 2nd Edition material can be used without significant changes in AD&D campaigns.)
To summarize, a Combat & Tactics's rock weighs 1 lb., is size Small, has a rate of fire of 2/round, and deals 1d3 points of bludgeoning damage to a Small or Man-sized target yet only 1d2 to a Large target. Its short/medium/long ranges are 2/4/6 like a dagger. Unsurprisingly, a rock is free.
This DM would be comfortable using these statistics in an AD&D campaign despite their provenance were a PC to pick up a rock and chuck it at Orcus. They're reasonable and unrewarding statistics for a commonly available free weapon. Further, this DM would penalize the PC's to-hit roll by whatever nonproficiency penalty the PC's class normally suffers unless the PC had the foresight to take rock as a weapon proficiency.
Note: This reader is unaware of a direct statement in AD&D that mandates proficiency in grenade-like weapon. Further, this DM never demanded such a proficiency from PCs in his campaigns, and this player never had a DM demand such a proficiency from his PC or the PCs in his party. That's not to say it's a bad idea, but it may very well be a house rule—which, by the way, is totally fine: every table has them. However, given this, the DM should make it clear at the campaign's outset that such a proficiency is necessary for proper use of grenade-like weapons lest tragic hilarity ensue.