Why would anyone translate it as ‘fell’?
One should ask the translators of the NIV, ESV, NASB, ISV, KJV, ASV, RSV, NRSV, NLT or the countless other translations that render it here as some form of “falling” or “fell”.

I’m going to make one last stab at this:

Yes, of course ginomai by itself doesn’t mean fall–we both know what a slavishly literal, word for word translation of genomenos prenes would look like; you need more of the text to determine that that is what is being described.

The expression could mean he simply lay down on his belly. It seems to me the only reason we deduce that this is describing someone falling or throwing himself down is the following details that he burst open and his entrails spilled out: the consensus seems to be–based on that added information–that this is a violent and forceful action and that the expression should be translated to reflect that, he didn’t simply come to be face down in some vague way, he *fell* face down. Yet even to take genomenos prenes as any sort of falling (whether head down or face down or while wearing a pink rhinestone jumpsuit) is already for the translator to impose an interpretation on the text. This is an interpretation *you also* impose on the text; in you opening salvo you ask: “Does the Greek text say he fell headlong, or fell face down?” and you state your thesis,” I argue the latter.” Well, if we are being slavish in our translation–if we are scrupulously avoiding imposing any interpretation, we must recognize that the text doesn’t say he fell at all; that is inferred by the translator–including you–from context. You condescendingly explain to me “becoming prone can be translated as ‘falling’ into the laying down position,” but obviously one can become prone without falling.

So here is once again what I have been trying to say:

If we determine that what is being described is that Judas throws himself down forcefully from a high place in an act of suicide, then ‘headlong’ is a perfectly acceptable translation. If I jump off a cliff such that I fall or land face down, I am jumping headlong–my head goes over the precipice before my backside (unless we imagine him doing some elaborate flips in the air). *If* we are confident that that is what is being described, then that is a perfectly defensible rendering.

Another, logically prior, question is whether the translator should impose any such interpretation at all, or should he instead regard the passage as inherently ambiguous and try to preserve that ambiguity in English–even if that results in a translation that is strange for his reader. If we decide that it is inherently ambiguous, enigmatic, and obscure, we ought to be slavishly literal, something like, “and having come to be face down he broke open in the middle and poured out all his inner parts”–preserve the ambiguity and let the reader consider the options. Heck, maybe someone will want to argue it is actually describing an emotional breakdown: he is overwrought with guilt, prostrates himself, “cracks open” (i.e., starts bawling like a baby) and “spills his guts”.

I am actually quite receptive to such a slavish translation in this case. If, after serious consideration and careful study, we say, “I just don’t know for sure what Luke is trying to say here,” then by all means don’t mislead the reader into thinking the text is clear when it isn’t. What is genuinely unclear should not be made clear by the translator. So again, *if* we are confident of what we being described, smoothing over the edges to give clear, natural, idiomatic English that describes just the same thing is not something I would find problematic; and as a matter of English, I don’t see a significant difference between saying someone killed himself by throwing himself down face down and saying he killed himself by throwing himself headlong, and so (on the assumption mentioned) I would not describe either as a mistranslation.

But again, this all hinges on whether we understand what the text is actually saying: we may not be comfortable admitting it (I mean of course a translator isn’t a commentator) but a good portion of competent translation is interpretation. Have you ever read a text translated by a person who really, fundamentally, simply didn’t understand what the text was saying? Have you ever tried translating an extended text where you really didn’t have the first clue what the author was actually tryin to say?

So going to the very first question: Your problem with the standard translations of the passage is not simply that they impose an interpretation (for your proposed interpretation does too, as do very many perfectly good translations of all sorts of texts–it is perfectly normal, in translation, to try first to understand the meaning of the text and only then try to decide how to put that meaning into the target language). Rather the objection is that those translations render the passage in a way the precludes your interpretation. But I don’t find your interpretation plausible, so I am not ready to concede that the standard translation is a mistranslation, at least not for the reason you propose–that the text is actually describing the decomposition of his corpse (I am still willing to consider translations that leave open alternative interpretations–e.g., that this was not suicide but divine retribution: he crumples over on the floor in pain then spontaneously bursts open–but that is another issue, and not the objection you are raising). You are, in other words, trying to bracket the question of interpretation as a secondary or discrete issue and simply accuse the standard translation of being a mistranslation, when in fact some level of interpretation naturally comes before translation and it is only to support your interpretation that you have any interest in changing the standard translation.

And as to my credentials: I never claimed my Greek was advanced (though the question at hand doesn’t hinge on obscure points of Greek grammar; grammatically the Greek is pretty straightforward). I do, however, have a lot of experience translating and correcting other people’s translations from another dead language, so these questions–what is the proper role of a translator, what are the difficulties translators face, and how should translators handle those difficulties–are questions I’ve spent many hours of my life being paid to think about.