When a parent sees someone mistreating their child, it's dangerous to underestimate the lengths they're willing to go to protect them.
Because when a person loves someone to that extent, it doesn't matter who is responsible for that cruelty. If they feel like a relative, their romantic partner, or even their own parents are causing harm to the ones they love the most, those sudden adversaries can often be surprised to see that they aren't the number one priority in that person's life.
And no matter how much the guilty party often tries to deny it, the secrecy with how they often carry out their malicious acts betrays exactly how aware they are that what they're doing is wrong.
But if one dad didn't happen to be in just the right place to hear one very revealing conversation, there's no telling how long his son would have to put up with what sounds like a pattern of awful treatment.