The pin holds a thing called the "spoon" in place. It's secured with a hole in either side of it as it attaches to the "neck" of the grenade where the pin going through it secures the spoon to the neck of the grenade.

When the pin is removed, the spoon is free to come away from the grenade. Usually this takes more than gravity, but not "too" much more. Sometimes the force of removing the pin is enough to rattle the spoon loose/off from the grenade neck, triggering the fuse, in the case of most frag grenades like the one pictured above, the fuse length is pre-cut to be around 4 seconds, until it reaches the payload of TNT at the core of the fragmentation casing, exploding.

[–] [email protected] 2 points 1 month ago

So if you squeeze the spoon to the body of the grenade and pull the pin, the countdown doesn’t start until after you throw it, correct? When the spoon comes off, those four seconds are roughly the amount of time it has to reach where it was thrown?