He walking in the dark,his head hit agaist a tree.

He walking in the dark,his head hit agaist a tree.
He walking in the dark,his head hit agaist a tree.

He walking in the dark,his head hit agaist a tree.
is.
hits

is。。。
hits

while he was walking in the dark,his head hit against a tree

不对。应为：Walking in the dark, his head hit against a tree. 前面为独立主格结构，作状语。