It's a streetfight theres no such thing as a sucker punch...If that guy was turned around drinking a coffee reading a newspaper and kimbo came out of nowhere and hit him like that, then yes that would be a sucker punch.....
In a fight expect anything, If kimbo would've picked up a brick and hit him then yeah that would be the sucker thing to do because the fight wouldn't be fair but the fight was fair and as a fighter one of the first things you learn is don't ever turn your back in a fight because you get left defenseless keep your gaurd up.
and some mma fighters have been trained since childhood. It's mixed martial arts, it isnt streetfighting/boxing it a whole different thing. Most mma fighters devote there whole life to it so of course kimbo would probaly
get his ass beat because he isnt a ninja 