if you are doing something ridiculous outside an officer's city limits (80+ in a 45 as an example, driving recklessly in a school zone, etc.), you bet your ass I'm doing my duty and pulling you over...that's what the mutual aid is for.

you're right that an officer shouldn't be doing minor traffic infractions and pulling people over for BS outside their jurisdiction, and I'm not sure what case the OP is talking about, but....there's mutual aid agreements for obvious reasons...even when it comes to traffic. almost every agency with a take home cruiser program that I can think of, has some sort of mutual aid with the neighboring cities. I know Hillsborough and Pinellas have them.

i highly doubt most officers are going to write a citation, at the most it will be a warning to tell you to knock off whatever behavior it is you're doing...but you have a duty to act if you see something dangerous.