Okay, I got this achievement this morning and unlike what the other solution says, it is NOT straight forward.
To clear a few things up first, you must win every fight by KO! TKO's do NOT count which means if you knock your opponent to the floor, don't follow them and let them stand up. You also can't finish by body shots such as a liver kick as they count as a TKO. Head strikes only I'm afraid.
Second thing to note is that you can't lose any fights. So even if you win enough fights by KO to clinch the title, unless you are also unbeaten you won't get the achievement.
Final thing to think about is to use the White Belt division as you only need 4 straight wins. When I did this achievement, I purposefully got my self relegated by losing each fight by KO. I just stood there and let my opponent belt me.
Now my solutionI used Anderson Silva and not Jon Jones as other solutions said. This is for two reasons. Number one is that his standard (
and
forward) head kicks are quick and powerful whereas Jon Jones' are quite slow and inaccurate. Second reason is that his ground and pound isn't too powerful.
This leads me on to how I guaranteed a KO. I practiced setting up my take downs and my ground transitions to mount. When in mount I would maintain position using
and
each time I could see my opponent was trying to escape. In between each escape attempt I would smash their face in with
or
.
As Anderson's ground and pound is fairly weak, I didn't need to worry about flash TKO's and could just work my opponent until their head was deep red.
Then I would allow them to stand up and deliver a swift kick to the head which would usually knock them out in one or two hits.
I hope you guys find this helpful, if you have any feedback please let me know and I can edit the solution.