Who are some Boxers who can't defend against the left hook? How to improve defense against the left hook?
Defense is really something that gets overcomplicated. You either get out of range of the hook or block it. If you aren't sure whether the hook is coming up to the head or body, just do your best to cover both with your right arm and glove, tuck your chin, and bite like hell on your mouth piece. If you notice that you are faster than your opponent, or see that he telegraphs the punch enough to time it, shoot a short straight right as he throws his hook. On the topic of fighters who had bad defense against left hooks, Hatton is one that comes to mind. All 3 of his losses came by knockout with the left hook, considering he had infamously bad defense.
Some bread and butter defense: a) Block it. Fast and easy. Will still hurt and possibly stagger. b) Duck under it. Preferable, since it leaves both your hand ready to counter. c) Biceps/shoulder stop. An old school technique. Unbalances and opponent and often breaks the flow of a potential combination. d) Step back. The exit button. Gets you nothing but more time. Different guards obviously mean different ways to defend. Bar drilling and practice, I don't see many ways to improve your defense against the punch. Good distance control and solid right hand (cross counters left hook; boxing 101) comes to mind.
Ali. Ali: Knocked on his ass when he was Clay in his 11th fight, against Sonny Banks. Punch was a left hook. Ali: Knocked on his ass when he was Clay in his 19th fight, against Henry Cooper. Punch was a left hook. Clay needed smelling salts in between rounds was the rumor. Ali: Knocked around all night by Joe Frazier and knocked on his ass in the fifteenth round. Punch was a left hook. I could go on but won't. Keep your right hand high, move towards your left are basic defenses.
Juan Manuel Marquez was always susceptible to getting clipped by a left hook. Barrera, Katsidis, Mayweather, and almost Bradley (12rd) dropped him with that punch