Plenty of times. Well, some failed and some successful.
One a guy with a knife cornered me for my phone and then chased after me like a minute later to get the unlock code, like, for real...
Another time, some gang of wankers saw me from around a corner and huddled around me. I was only like 11 and was a pretty shy kid, so I didn't stand a chance and handed over my phone and wallet. My brother found me like a minute later, as I was walking in home with tears rolling down my face. He chased after them with a golf club
Another time, I was on the bus and I saw down. Instantly, the guy sitting in front of me got up and sat beside me. The outside seat. I knew he was trying something. I was putting my wallet away and he tried to lunge for it. THANKFULLY he was an idiot and kind of backed away when I showed some force, but also other people on the bus saw him and called him out instantly. They then got me to sit by them until I got to my destination, which was absolutely wonderful.
Ummm, the funniest was this guy who came up to me and said, "GIMME YOUR PHONE" and I went "No", pushed him aside and stared him down. He legit RAN down the road away from me
Another time (omg, I know), the guy from the bus (YES, THE SAME CRACKHEAD) came into a cafe with my friends and sat down next to us (3 people at a four person table) and said he'd do something if we didn't hand over our stuff. Luckily, there was an old man next to us, throwing bread, feeding pigeons and I SWEAR, at the exact moment he said that to us, a pigeon landed next to my friend who DESPISES them and he let out the BIGGEST scream ever, which only drew everyone's eyes to the robber, who thought it was because of him

The manager ran out and I got up and was like, "He's trying to rob us!". They kicked his ass out and he tried taking someone's phone outside the cafe then, but the manager had an eye on him and shooed him away. SCUM!
Ermmm, I think that's it tbh....
Once I actually rescued a girl though? I was waiting for a bus home in Starbucks and using the toilet, this rough looking woman came in the queue. She seemed nice but I had my eye on her. So I went out, back to my table with my friends. I noticed this girl on her own in the corner on her laptop. Minutes later, who goes to sit by her, but that rough looking woman. So I kinda know something is up. She starts taking out some stuff and I'm like, "Maybe I was wrong", but I still keep watching. I look back a minute later and the woman is standing over the girl, threatening her, and she glances at me with such fear! I SHOT up and was like, "WTF ARE YOU DOING?!" and she got such a shock, because most don't expect retaliation and she started backing up and I basically was like, GTFO! And made sure she left the premises! I then went back to the girl and told her to maybe move to a busier area, in case she came back. She was foreign too, god love her! Some people
