Actually, you're wrong. Standard issue US military grenades come with 2 safety measures. The pin, which is pulled first, is the first. The second is the spoon, which is the little curved handle that flips off when the grenade is tossed. The grenade won't detonate until that spoon is triggered.
I'd like to point out that it's possible to release the lever without throwing the grenade. Normally, one would press the lever with their palm against the grenade body while pulling the pin, but someone could hold the body of the grenade and wrestle the pin out.
There's actually three safety measures on a military grenade. There's a small, metal clip over the spoon, then the pin, then the spoon itself. You can, however, release just enough pressure off the spoon to start the fuse.
Back to the original point, I'd also like to point out the practice of "cooking" a grenade; intentionally releasing the lever while holding the grenade so that you can throw it with a shorter time fuse. Usually done to prevent the throwing-back of the grenade or allowing it to explode above ground so that the blast is a bit more spread.
That is on point, and very dangerous. Grenades typically have a 3-5 second fuse...I have never cooked a grenade, but I have thrown a grenade that went twenty feet and exploded and then one that went about five feet and exploded. Extremely terrifying, haha.
Oh...I see