In 40+ years of travel, I have only had one incident where I felt I could have been mugged.
As I changed money at a Paris railway station, I realised I was being observed. Worse, the group of three followed me onto the metro and into my carriage.
They then carefully watched me at each station to see when I got off the train.
I spontaneously hopped off the train at a busy station just as the doors were closing. They jumped off too and trailed me down the platform to the exit.
I turned around and staring at them directly said “Non”.
If someone attacks you, shout out “No!” as loudly as you can. Or “Nein”, “Non”, “La”, “Lo”, depending on the language of the place you are in.
Saying “No”, is more powerful than yelling “Help” .
“Help” suggests that you are weak or helpless, a message that attackers feed upon whereas “No!” is powerful.
In my Paris incident, the effect was immediate. The group looked shocked, on lookers on the platform became interested and I felt I had taken control of the situation.
The group scattered and I continued on my way unmolested.