After being interrupted by the character he is talking to, the nameless MC says the following line of dialogue, referencing a situation that the character he is currently speaking with acted in.
"......why do that sort of thing, from a while ago?"
The translation of Japanese to English doesn't sound truly right to my ears, even though it makes perfect sense when considering that the MC has no clue as to what is going on around him.
To break down the sentence so that those who are not learning or understand Japanese can help, the following are the basic semantics of Japanese that are used in the above sentence:
は is a topic particle, the topic being denoted by whatever is before it; in the above case, that would be "さっき", or "A while ago". で in this case, is added to the 何, forming 何で, which generally means "why" or "how". あんな I believe means this when considering the context of the MC not understanding what was occurring during the situation. Therefore, I translated あんな to the English equivalent -or as close to a equivalent I can make, as its impossible to translate perfectly from one language to another- of "sort of" or "such". こと in this case can translate to "thing" or "situation" but I think it specifically means 'situation' in the above case. To make the English seem more natural, and to keep the vagueness of the original, I went with "thing", as "Why do that sort of situation?" is something a native English speaker would never say. The を (wo) at the end is something I myself am still trying to figure out, but this answer has providing some meaning to what its doing, I still don't know what that is in my specific case.
Maybe its because in America (as far as I'm aware) we don't ask questions that are vaguely questioning AND specific without some sort of emotional emphasis; such as, "What the hell was that?!" or "Why in the world would you do that?".
I'm trying to figure out a away to keep what I think is the subtle meaning of 'why did you (and others) do that sort of thing' in my translation, which is why my first translation attempt is vague in terms of the 'who' that is doing the 'thing'.