Sorry, but I have to blow the whistle on this one. Most grenade fuses only last 4-5 seconds total, and some of that is used up in throwing time and the momnet it takes for the target to realize that a grenade has entered their position. That cuts it down to somewhere between 1 and 3 seconds to act, and that's if the enemy threw it without holding onto it an extra second or two to reduce thyour available reaction time.
If you're clustered in a fighting position with your buddies and a grenade rolls in, you all have to get at least five meters from it to get out of the kill zone, while under fire...in 1 to 3 seconds. Or somebody can jump on it. Unless they react quickly enough to throw it back, that's the choice.
BTW, what's the origin of your screen name?
I’m from the peacetime army where the live grenades were most likely dropped at the feet of someone who had just screwed up.
Of the several accidents I heard of, one was an instructor who accidentally pulled the safety of a grenade on his belt, and was so blase about the whole thing, he didn’t even try to pull it off and throw it, just saying “That’s the sort of dumb thing only a trainee would do”, before being killed.
Another was of a Captain safety officer on a grenade range who walked out onto the range to pick up an UXB, and was carrying it back when it exploded.
Lastly was a soldier who took apart a dud to find out why it hadn’t exploded.
For a while there I thought that every time you were issued a grenade, you temporarily lost 10 IQ points.