Nut. Shot.

This is my theory.

Maybe it happens when the enemy has a kevlar vest on?

isn't it the shot grenade icon, when you shoot the grenade the the guy has thrown at you, i.e they throw a grenade and you shoot it, this causes it to explode in mid air, if this happens close enough to an oposing player BOOM they are dead. do you have the shoot grenade ability enabled? and do you have the achievement for killing someone that way?

Because I also want to know what this is, I am replying.

it is a nut shot.
For sure.

Even if it isn't a nut shot, it's really a nut shot. Who wants to inform Splash Damage?

It is the nut shot I just shot somoene in the balls with the sniper and the symbol came up

I assumed it was grenade shooting.

I don't have that ability and I get it on occasion.