I had a situation come up in the game last night where an NPC threw a frag grenade at the party (who were taking cover behind a door) and didn't make the Ranged (Light) check, with a simple failure.
I was wondering what would happen narratively in this case, with advantage, threat or just simple failure. Does the grenade go off, or not?
In the case I had, I said that the grenade bounced away and detonated harmlessly away from the combatants, but was unsure if that was the best call.