from my experience this is how most ppl in the street attack you.I walked into someone by accident and as i was apologising(mind was disengaged) he threw a combination of punches at me.The attack shocked me because i wasnt expecting it .Luckily the punches didnt do major damage and i was able to fight back.
Now if those punches landed on my jaw etc i would be probably be KO'ed.
So how can you avoid being sucker punched?i dont want something like this to happen again