Happa wo kakeru is a Japanese phrase meaning, roughly, to bait or insult someone into trying harder. I had always assumed that the happa was the common Japanese word meaning "leaf" or "leaves", and that the whole phrase was some opaque idiom. But the other day I saw the word in print for the first time; it turns out that happa is 発破, a Sino-Japanese word meaning "[controlled] explosion". The original, literal meaning of happa wo kakeru is "set off an explosion," so the metaphorical meaning is quite transparent and roughly equivalent to "light a fire under [someone]" in English.

Once the initial wave of embarrassment had passed, it occurred to me that this might count as an eggcorn. It clearly isn't just a spelling error, either — I really thought that the word was "leaf". And it's structurally equivalent to accepted eggcorns like "way anchor" and "preying mantis". The one snag might be that the "leaf" interpretation of happa wo kakeru doesn't actually make sense. I mean, I assumed that it did; as noted above, I figured the literal meaning "put leaves on someone" somehow idiomatically meant "insult someone into better performance." But I never actually wondered about the specifics.

So is it just a sort of written malapropism? Maybe, but I've always thought of those as isolated errors by an individual, and Google claims to have over a million hits for 葉っぱをかける (the "leaf" version of happa wo kakeru).

That's twice as many as Google claims to have for the correct version, 発破をかける, incidentally. Of course Google hit counts aren't accurate enough to meaningfully compare in situations like this, but it seems quite likely that the "leaf" interpretation is more common than the correct one. Yeah, I'm calling this an eggcorn.