Hi,
Swint grabbed Herman by the hair atop his head so that Herman had no choice but to trot along with him while Swint ran down Main Street.
The word 'atop' does not seem very natural to me. I suggest simply 'by the hair atop his head'. It will normally just be assumed that the hair is on his head. ( We seldom, for example, grab people by the hair on other parts of their body.
)
I don't like the way the sentence is constructed. It seems to describe a dramatic event in an undramatic way. I suggest this.
Swint grabbed Herman by the hair and ran down Main Street. Herman had no choice but to trot along.
Best wishes again, Clive