This grenade explodes after a character pulls the pin, meaning that he has to hold it on hand. If you throw it, it will explode.
The trick behind this is very easy: just create two dat.-files for the grenade. The first has an id-number between 100 and 199, so it'll fall from the sky. The only important thing in this dat.-file is that you use state: 8000 in the on_hand frames, so it'll transform into the second dat.-file once it's picked up (this weapon shouldn't fall from the sky!). In this second dat.-file you just modify the on_ground frames - note an opoint for an explosion. That's all!

The grenade was originally made by Doenerdevil, but I copied the dat.-files and the sprites and modified them a bit, because the code was kinda old. But the grenade-download in the download-section is unmodified:

Grenade Download now!

Inspired by Doenerdevil