Love this analysis and the slowed down gifs and how they almost seem to show Billy happening upon dishes and it reminding him of that moment in the kitchen between his parents.
Given that Billy’s happiest memory and the thing that either was his retreat that El found him in or that the beach with his mother war the light that saved him, I would guess that Billy spent unconsciously mirror his mother.
Billy subconsciously or consciously mirrors his mother often. The way Billy and his mother are dressed in these scenes is also a direct parallel: red top and jeans. I could be wrong, but I also think both Neil and Steve are dressed in gray tops.
Not to mention, Billy works out. Often. He’s stronger than Steve maybe even stronger than Neil. That’s to say, Billy has the skills and the ability to stop Neil. Importantly: he doesn’t.
It’s critical that the difference between Billy and his mother seems to be aim. One could assume that maybe she didn’t want to hurt Neil? Maybe she just make him to step away from her and Billy. Reactive violence is common in DV households. However, it’s possible that she missed in this instance and has hurt Neil before, in self defense.
That could explain why Neil keeps such control on Billy and ensures he is too dispirited and afraid to ever hit him back. When he grabs Billy’s head and repositions it in the bedroom scene, he points at Billy like he’s a dog, as if to tell him stay where I put you.
From context clues and the Dacre interview, one could assume that Billy sees Steve as Neil in this moment and part of the reason he beats him as he does is because Billy can’t fight bald or stand up to Neil. But he sure as shit can stand up to Steve.
This is a classic wrong place wrong time. Steve reminded Billy of his abuser (Neil) and triggered something akin to a psychological breakdown.
Another thing to add is that someone else was in the top scene. Young Billy.
If his mother was protecting herself and her son, ask yourself: Who is Billy protecting?
Billy is protecting Max in this scene.
Steve is the stand in for Neil and the abuser in this situation and in Billy’s mind, he’s not only protecting himself and his mother who left him, but he’s also protecting Max.