MCRP 12-10B.1, page 186

dangerous, and extreme caution and common sense should be used. In most situations, throwing a grenade up a staircase is not recommended. (Again, the grenade is being used in the initial building entry or clearing of the bottom floor of a building having a staircase.) If a grenade is thrown too hard or the staircase is too steep, the grenade can roll back down the staircase. For this reason, if a grenade is thrown, it should be thrown underhand to reduce the risk of it bouncing back and rolling down the stairs. A nonverbal or, as appropriate, voice alert is used when throwing the grenade. Once the first grenade has detonated, another grenade should be thrown over and behind the staircase banister and into the hallway, destroying any enemy hiding to the rear. Figure A-27. Entering Through a Breached Hole Figure A-28. Tossing a Grenade Up a Stairway Military Operations on Urbanized Terrain A - 25