B-Hop relies on his counter right a lot, but the hook is always there if he can land the right solidly first. I think he's always had a good left hand, just not his primary weapon.
It's not that his left hand improved, it's that he was facing a squared-up opponent who gave Hopkins good angles to land left hooks on. Fighting a southpaw like Tarver or Calzaghe, not so easy to get the left in.
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