Parents should try to understand that support is a great way to build confidence. This is vital to building discipline and a stronger relationship between parent and son/daughter. In the movie Billingsleys dad takes it to a whole different level. He wants everything Donnie does to be absolutely perfect, ultimately trying to live within his son. Donnies dad finds the need to humiliate and harass his own son in order to build some sort of toughness, and expects that this method will make him play better. This is definitely not the way to solve the problems Don was having on the football field.
I understand that his dad was a drunk with an attitude problem, but that certainly does not give him the right to treat Billingsley that way. Just imagine the frustration and discouragement building inside of Donnie. Trying to have fun playing football must have been near to impossible for him. Donnie probably had a lot of negative emotions and tons of pressure while playing, worrying how his father would react to not living up to his expectations. Any mishaps Donnie would have on the field should have been left for his coach to address, not his dad. His dad should have played his part as a loving parent and supported his son, no matter the outcome.