While I will give you the fact that many boxers do not do well in UFC. Mike Tyson is not just an average boxer, how many top Heavyweight boxers have you seeen fighting in the UFC???
As far as the other comments made earlier by others about Tyson's street fighting abilities. He grew up on the streets for many years. I'm sure he knows how to handle himself in that situation as well.
There was one well known street fight he got into with a former boxer by the name of Mitch Green whom he fought earlier in his career. Tyson hit the guy one time in a club and broke his nose and blackened the shit out of his eye and his cheek. The whole side of his face looked like it had been hit with a baseball bat. This was from one punch with no gloves on and this was thrown at a guy who was a top heavyweight boxer at that time. So you guys that say you can beat Mike Tyson's ass can hang it up, your just talking shit!!!
No heavyweight in the world ever has had as much raw talent as Tyson. No one could match his speed, strength, chin, or
determination.