to get this achievement you need to get Killing blows with your ultimate Gravitic Flux
the way i got it is when the enemy team is injured from defending the king of the hill pop it or when they are regrouping while critically injured,
but you just need to get the killing blow so even if you kill someone with the ultimate with out slamming them onto the ground it will count so if you play the objective you can get this if the enemy team doesnt have a healer or a good one, but watch the enemies health if they look low enough for it then pop it, but say if the enemies still have health on them? use your balls to injure them just a slight amount the catch is that there is a small window for you to hit your shot with the balls before it ends and you can let your team mates injure them up in the air before it ends but just hope they dont get the kill credit