From Chapter 20 - A Hero’s Imperative:
While Ma Guangzuo was calling and hollering, he was making his way
slowly towards Fawang. Suddenly, he threw out a fist and struck the back
of Fawang’s head. With Fawang’s abilities, this sneaky attack of Ma
Guangzuo’s would never have succeeded; but at this moment in time, he
was just concentrating on Yang Guo, Xiaoxiang Zi and the others. The
idiot he had ignored actually managed to strike him on the back of his
head. This attack was hammer like; hammering him into a starry daze. In
his anger, Fawang sent his elbow backwards striking Ma Guangzuo squarely
in the chest. Ma Guangzuo called out and his body fell forward right
onto the shoulders of Fawang. Fawang’s legs bent a little and he dashed
straight down the mountainside.
That's right, Ma Guangzuo fetched him one on the back of his head.