Ok so this one is quite easy to do you can have it done in a few hours and even faster if you have a friend to do it with. To get a point towards this medal you have to shoot an enemy grenade that has been tagged to the wall or the ground and you need 1000 of these for the onyx.
I did this on Gridlock; you want to, in the weapon set up, put everything to incendiary Grenades and if you’re doing this on your own then do capture the leader with a 2nd controller and no bots and rounds to win max. I had a little circle that I ran in, I started in the centre of the level there are some grenades there in a circle of cars moving up I planted one on the car then one on the corner of the wall, Then grabbed the grenades in the arch way in the upper centre of the level, Then ran to the right and planted them on the wall near the steps, Then I ran up the steps to the back of the level got those grenades planted them in the same place as the last two, Then from there run straight down to the bottom of the level to the grenades there and plant one of them on the car you go past to get them and one on the floor then back to the start.
Remember to have the weapon Respawn “after pick up” this way depending on how quick you run round you shouldn’t have to wait for the grenades to Respawn they should appear just before you get to them. Also of course you can only tag two grenades at a time so you want player 2 doing the tagging and player one in the centre of the circle Player 2 is running and every time you tag two grenades swap controllers shoot the grenades and bam 2 points towards your medal. If you run out of ammo you can just capture the leader and start another round with a full clip. Rinse and repeat.
I believe this is one of the quickest ways of getting this medal as in real play I almost never spot a grenade to shoot and get a legitimate point; I only really notice I’m near an enemy grenade when I hear the beep beep boom! … and by this point it’s to late.
If you have two people, doing this is even quicker, you can just run all over the level one person tagging, the other chasing after shooting the grenades as they are tagged.
Hope this was helpful