Without sources or much of a doubt either way I suggest that this is falling out of line.
Unless the idioms were largely unrelated with the verb to fall, they must have begun with falling to the ground for whatever reason, which disrupts the line: cp. Ger. ausfallen; see also Old Frisian ursittan "to fail to be present", urfaran "pass away, die" for the prefix.
Your source vouches that the idiom is indeed related to the common verb, though I take that with a pinch of salt. Within German we also find ausfällig "verbaly abusive" (chiefly collocated with aspectual werden), vice-versa gefällig, Gefallen "favour", and the (quite recent) research history of the root is difficult.
Maybe Swedish úrfelli "skyfall" or Icelandic úrfellingar "of an omission, of a cut", Dutch vervallen "having no legal force or cogency, invalid" etc. also belong here. Don't make me sort this out. You see, out ~ aus ~ ur and ver- are plausible correspondances (PIE *ud-, *ud-s) but not the only source of ur in the theory formerly known as Urindogermanic (PIE). All they have in common in the latter case would be the intensive reading of out, which might be enough to warrant a calque in English. That makes it fairly difficult to trace. In particular, I think it is quite likely that another root become in some way corrupted, seeing that the reconstruction *h₃orǵʰ-, *h₃erǵʰ- "to copulate" > *argaz* (Kroonen, 2013) suggests probable cause. That'd be OE earg, E. arg, erie, Scotts ergh, erfe, erf (en.Wiktionary). Nowadays we rather fall in love, but German in Liebe verfallen still bears the connotation of temptation, which may be due to French fyr-.
In any event, it is not very difficult to go from failure to perform to an argument about the failure and eventually to a fight, if the initial weakness is seen as a disgrace. Still, one would like to see quotations to prove it.