Two things need to be clarified by the host: Proximity or BB Strike for hit, and what is classified as a grenade.
If you have to be hit by the BB, cover will help. If it's proximity (or room), then you're dead when the grenade goes off in the room.
The second part is really important... You see less of it in CQB compared to outdoors... but classification of a grenade is important. A tornado, loaded, and gassed; when detonated is a grenade. A tornado, unloaded, ungassed, or otherwise not working: It is not a grenade, it looks like one, but it is not.
If someone throws a grenade in the room with me, and it doesn't go off (no bb's flying), do not expect me to call it.
Ár skal rísa, sá er annars vill
fé eða fjör hafa. Sjaldan liggjandi úlfur
lær um getur né sofandi maður sigur.