I agree as those out and about are quite likely worse the wear for drink and/or drugs, just as I was in my misspent youth. Or there could be teenage gang members looking for trouble. At that time there is always an increased risk of trouble/violence just as in any Western city. But generally Udon is very peaceful with any violence being Thai on Thai. There was one exception that I know of though which must have been about 10 years ago now, when 2 farangs were attacked and killed by a couple of Thai men while just sitting and chatting in Nong Prajak park at about 4am. I recall reading later that it was a copycat attack of the controversial murders of 2 young backpackers on Koh Tao which is well known as Death Island....Dont go there!