My research into ancient Greek Pankration introduced me to the Hammerfist strike and it is my humble opinion that while the ptimum striking surface is the hand its almost as effective even halfway down the forwarm. This is what makes it such a unique strike , this uyse of the whole arm feeds directly into the switch from striking range to grappling range.
This can be done with or without step as described but also can be done across the body, with small chopping movements almost like a jab or even done doubly if you are feeling fancy. This strike was known as the chopper in Pugilism.
You can see many examples of the preparation to Hammerfist in the striknig archives on this site.
Historical Pankration Project I will be working on an article focused on the Hammerfist and its use in Pankration in the coming months , when I do I will post it here. I will try to provide some video with it to help with explanation.