I have managed to do it twice but neither time counted. the first time was literally the last kill of the match, the second was an enemy hog and it told me I killed them with a hog.
It is literally impossible for me to do, and camping near a cliff with a repulser just gets me flanked and blown up as no one is dumb enough to stand near a cliff.
Make sure your doing Arena. Training yard has two spots, and recharge has a good one where the hammer/sword spawns.
Other option is to keep your challenges in mind, but don’t get to hyper focused on them and just enjoy the game.
The problem is that the whole progression system is based on challenges, like it or not, people tend to end up focusing on them.
It is an endless cycle:
There are global statistics in social games. → I ignore the challenges because I want to play well and not tarnish my statistics → After a while I get frustrated because I do not advance in the pass and I do not get any cosmetics or items for my Spartan → I want to do the challenges but it overwhelms me because they are challenges that hurt my statistics or are difficult to do. → I do not decide to do them but I still do not feel that I have real progress → repeating this feeling of overwhelm indefinitely