We seem to be getting a lot of stories lately of folks inserting themselves into a situation before force is required, prompting a hostile response, and being then compelled to threaten or use force.
Had I been in this situation, I would have called 911. I would not have intervened unless and until there appeared to be threat to life or limb.
What was witnessed, before intervention, was at worst a simple assault. Once the full facts of the situation were known, it could turn out to be no crime on the man's part at all. Although this is highly unlikely, it is possible and, if true, it means that the man was prompted to assault the interloper, leading to the tasing, which might otherwise not have been necessary.
I hope that folks that OC don't see themselves as needing to insert themselves in every fracas that erupts. Personally, I won't insert
myself into a situation unless I am sure that there is a threat to life or limb. Time permitting, I will always call 911 first.