Please keep in mind that I have had no training at all when it comes to animation, so this is all a product of me winging it with no proper knowledge.
The first of two test animations I did when applying for the Skullgirls game project. They provided the first keyframe and a rough one at the extent of the kick. Instructions were to do two or three frames before the kick keyframe, and then three on the return to idle.
Keep in mind that this is a fighter, and the frames are not meant to be slow and fluid before the hit, as it is meant to be quick and have impact. Also, the frame speed of this gif shouldn't be taken into account, as the focus was on the frames; the speed would be adjusted as need-be in the game.