crumble
Collapse and Crumble are two possible words.
That looks a bit like the word disintegrate which means to break down into small pieces or fall apart.
The verb form of "disintegration" is "disintegrate." It means to break down or fall apart into smaller parts or components.
It falls and break
collapse.
fall of a chair or down the stair
The only thing wrong with this sentence is that both parts of the sentence are in present perfect. Rewriting the sentence without contractions: "He has gone down, and he has not put his hands out to break his fall". One wouldn't say this. One would say, "He has gone down, and he did not put his hands out to break his fall"; or "He went down, and he did not put his hands out to break his fall".
You can, it means to fall helplessly down
If you fall down, you can break your neck.
It falls and break
sure, if you fall wrong you will break it
because it is a word and it means to go down or a fall in wrestling