This is a line from a sports manga (soccer), after a rather unusual shoot, but I can't seem to make sense of it:
そんなのアリかよ!?
I have no idea what the "ari" in here refers to? Is this some slang? Some short form of an idiom? It certainly doesn't seem to be related to any ant...
Thanks in advance!!
「アリ」 here means "acceptable", "no problem", "possible", etc.
It is a vastly common colloquial usage, but I would not call it slangy.
「そんなのアリかよ？」
therefore means:
"Is that (even) acceptable?"
Needless to say, the word comes from 「有{あ}り」 and it is pronounced differently from 「アリ」 ("an ant").
「アリ」 in question is 「アリ{HL}」.
「アリ」 ("an ant") is 「アリ{LH}」.
There used to be a TV program named 「コレってアリですか？」 ("Is this acceptable?") and surely enough, the program's mascot was an ant for the pun of it!
「あり」is a pretty old style of the flexion of a transitive verb,「ある,」meaning “be,” “exist” and “lie.” 「池のほとりに一本の梅の木あり」means “There is (stands) a plum tree near the pond.” 「ほかならぬ理由あり」 means “There is a certain reason (for doing that)”
You’ll see「訳あり商品」displayed in a store front quite often at supermarkets, department stores and most of retail stores, which means the products with a certain defect such as a small scar, stain, scratch on the suface of a product, or a product nearing the pull date.「訳あり」in this case means there IS a certain reason for selling the product for very low price.
When you're driving in resort places like the Izu Peninsula and the Hokone highlands, you'll see a lot of signs reading "空き部屋あり" in front of hotels and B&Bs, which means "Rooms available."
Also 「何（なん）でもあり」is a very popular wording, which means "Anything is possible / Anything will do."
「そんなのありかよ」means “Yikes, Can it be possible?” Again, 「あり」here denotes “IS it possible, (acceptable, allowable, permissible) on the earth?”
