It's just petty crime. Bag snatching , pick pockets, etc
Violent crime on foreigners is kinda rare unless you get involved with street hookers and get held up in the hotel room.
Viet on Viet violence is a thing though. I was with my wife at the Buddhist theme park in Saigon and a grab driver was being attacked by a group of men with big bamboo poles. Nothing to do with us but it was pretty scary. We quickly got the hell out of there.