Similar to "Jump the Shark" or "nuke the fridge", this idiom is used to describe when a videogame has begun its decadence or a period of bad quality. Named after the events in the final level of Resident Evil 5 when Chris Redfield shows impossible levels of human strength when he punches a boulder in a freaking volcano. It's important to mention that these moments aren't guilty of the changing direction (for worse) of a videogame saga but rather a symbol of it.
Oh my gosh, I thought this game was just campy but after the cutscenes it has definitely came to its "Punch the boulder" moment.
The video game equivalent to "Jump the Shark" (TV series) and "Nuke the fridge" (movies) describing a bizarre/ridiculous event in a work or franchise after which it all went downhill. Most people tend to just use "Jump the shark" for all media because our brain space is limited. Originates from Resident Evil 5 (a series which ironically came back strong with part 7).
They made Sonic kiss a human princess?!? It couldn't possibly punch the boulder any harder, what were they thinking???