Thrown explosive

A thrown explosive is a type of weapon that has existed in some shape or form in every Fallout game.

Fallout, Fallout 2, Fallout: Tactics
In Fallout, Fallout 2, and Fallout Tactics thrown explosives are governed by the Throwing skill.

Fallout 3, Fallout: New Vegas
In Fallout 3, thrown explosives are moved into their own skill category, Explosives, including also the Dynamite and Plastic explosives from Traps.

In Fallout: New Vegas, thrown explosives are still governed by the Explosives skill. The Explosives skill in general is broadened to also include "explosive"-style guns, but extra traits and perks are included that help differentiate thrown explosives from other explosive weapons.

In V.A.T.S.
Along with Melee weapons and Unarmed, targeting individual limbs with thrown explosives is impossible. Moreover, because thrown explosives have a finite range (again, much like close-ranged melee/unarmed weapons), a step or two in the wrong direction can change a moderately good chance of hitting to a 0%.

Even with a 95% chance to hit, this in large part means that - by the game's calculations - the explosive component of the weapon will have a 95% chance to hit. This means that an enemy on a narrow ledge, for example, may be virtually impossible to hit despite a high projected chance: the game frequently assumes that the grenade will be able to land on a surface near or under the enemy so as to connect the explosion with the target.

Moreover, when throwing an explosive in V.A.T.S., the projectile follows a parabolic arc. This has the side effect that shots with a high chance to hit may still miss in certain situations. For example, throwing a grenade at a far target when standing right behind a doorway will almost guarantee that the grenade itself will hit the top of the doorway and fall right in front of the player. This is not too much of a significant issue in Fallout 3 where players only take 10% normal damage in V.A.T.S., enemies are more aggressively slown down, and frag grenades virtually infinite. This becomes a more significant issue in Fallout: New Vegas when the player takes a much more significant fraction of normal damage (75%) and enemies are better able to close the distance in the time spent waiting for the botched grenade to explode.

Fallout: New Vegas thrown explosives
Fallout: New Vegas Thrown Explosive weapons, 2