So let me get this straight. The defenceless daughter gets beaten black and blue by a boxer, so the retarded father decides to train and have a fair fistfight with said boxer, he didn't even beat him up as hard as he beat his daughter.
This shouldn't be tagged as seinen imo. In a seinen the father would either just fuck up the little shit in a dark alley with no regards to the means, or pay somebody to do his job. Depending on how dark it is the guy would either be killed or made an invalid. In this manga we see a typical unrealistic shounen development.