I once tackled a guy that the Milwaukee Police were chasing, I kept him in a "Full-Nelson" wrestling hold until the cop made it down to us.
I was at work on Farwell avenue, and I heard someone running across the roof of the building I was in, I went out the door as the guy was jumping down, A cop was at the fence yelling to grab him. I chased, caught, and took the guy down.
He was being chased because he was caught peeking in a womans window, they were looking for this guy for weeks due to his stalking & peeping history.
I do not consider that a citizens arrest, just slowing a guy down to helpfacilitate his apprehension.
Another time I was by Grand Avenue mall, in heavy traffic between Michigan Ave & Wisconsin Ave. and I saw a guy running away from 2 cops while handcuffed behind his back, my foot accidentally slipped off the brake pedal as he crossed in front of my car
, he got caught right in front of me.