fistfight vs go at it

fistfight

verb

To fight using bare fists.

noun

A fight using bare fists.

go at it

verb

To fight.
To engage in some activity, especially vigorously or enthusiastically.
To have sex.
As go at + it; spoken emphasis typically on 'go'.

How often have the words fistfight and go at it occurred in a corpus of books? (source: Google Ngram Viewer )