Well from my boxing days, I never jabbed when my opponent is way to close in my punching range and crouching low, its a obvious set up for a devastating hook counter.
The jab is one of the most accurate and useful punches you can throw. It also helps to setup your punches and get off those flash combinations. A great jab can nullify a faster fighter, and stop an aggressive fighter from being overly aggressive. I wouldnt advice any fighter to not use it, exept if your fighting on the inside.
It can be harder to jab effectively against someone in the opposite stance, especially if they have the superior foot position/body angle.
From my fighting days the only time I didn't throw as many jabs was when I was fighting a southpaw but with that said, I still threw a lot of jabs as most fighters do. Against southpaws I would feint jabs and throw lead right hands but again, I still threw a healthy amount of jabs mostly to check a southpaws jab as opposed to using the jab to set up my punches like I would against a conventional fighter.
Versus a southpaw refusing to use the jab and instead receiving/attacking your oponents with huge straight right hands is a valid strategy. You should still use your lead hand for control tasks, though, jab or no jab (left hook is very popular too, running away from your oponent's strong hand). This strategy usually results in huge head clashes (specially if both fighters choose to use it), so you need to be careful and, even if you are, probably you both will end with a cut.
Lewis packed a nice punch his jab. These days Devon Haney has a great jab. Also how many times was Oscar doubted ''knowing it was the night (for the right time) of the jabs.''
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