Need Help about anatomy of human here (newbie artist)

Oktaviart

I need some advice here...  i want to make some of 2 character fight each other... i kinda struggling with i circle red one... it seems like some anatomy broken here... but i cant do much... before i posted here... iam already watch about reference everywhere.. but i can find it, the reference i want... or there some good keyword for me to use it in google.