Sometimes its difficult to form patterns but if you look at some of these top notch fighter's overall book of performance and look at their failures, though far and few between, you can find common threads.
For example, some of my NY favorites who you have seen alot of:
Chris Simon- Chris seemed to have problems with Tall, lanky fighters with a
good reach. IE (Chris McAlister,
Mark Janssens,
Zdeno Chara,
Derek Boogard,
Sandy McCarthy etc.) Off course this wasn't
always 100 proof either as it depended on the fighter but he did
have more of a problem in this area than normal.
Another problem for Simon on occasion was his balance.
It seemed in some of his bigger battles with stronger
opponents, he would wind up on the bottom.
Nick Fotiu- Nick had more of a problem with quick handed fighters.
IE(Bob Nystrom, Jack MacIlargey,
Joe Paterson etc.)
Again, it depended on the level of the fighter.
Clark Gillies- Big
Behn Wilson was definitely in his head but Big Behn's
weapon of choice was the best uppercut in hockey. When Gillies
fought
Lyndon Byers late in his career, he had several tough
fights with him. Lyndon's weapon of choice was the second
best uppercut in hockey. I noticed that in tight,
Clark sometimes had a habit of dropping his head.