傷つけられ追い詰められたノラ犬は、人に襲いかかることだって、ある。
There are even times when a wounded and cornered stray dog will attack a human.
In my TL I have guessed that ことだって、ある is ことがある (there are times when...) with the が being replaced by だって to give the meaning "there are even times when...". Is this correct? Why is there a comma here?
My other thought was that って might be quoting the stuff before it, but I got stuck with that line of reasoning.
You have got this one correct.
「Verb Phrase or Mini-Sentence + ことだって、ある」
means:
"There are also/even times when ~~~."
It is sayig that ~~~ is totally possible. 「～～だって」 basically means 「～～もやはり」.
The comma there is unnecessary and it is usually not used at all. The author might have had a reason for using a comma, but without further context, we could not be certain of it. Most likely, it was for emphasizing the fact that the stray dogs actually could attack humans at times.
NOTE: This 「だって」 should not be confused with the sentence-ending 「～～～だって」, which is quotative. "~~~~, he said.", "~~~, it says", etc.
