Not sure if I understand correctly, because skill descriptions rarely make any sense lately, but if snapper bone is disrupted during his charging phase his physical damage will be reduced by the exact value of the physical damage skill. So why go through all the hustle of making such an elaborate description, when you could have said that his attack fails and does no damage if he's disrupted? So, is that description accurate and he's supposed to do no damage or the deduction value should have been a lower number?
P.S. Paying attention to numbers when upgrading the skill, it seems attack value gets raised by 144 and should be lowered when disrupted by 84. So he should still do around 40% damage even if disrupted, but in the end both numbers are the same, which completely negates his attack.