跳び箱 as a synonym for a obstacle? I've been trying to understand lyrics of a j-pop song by Utada Hikaru. It's your typical pop fare, with a healthy dose of unrequited love and self-affirmation. At one point in lyrics, however, the story takes a weird turn: …(!) … What is that _vaulting horse_ doing there?! The naive interpretation is that the whole story is happening in a school setting, and it's a literal reference. I'm guessing that might have been used to mean an obstacle/hurdle to overcome - together with subsequent practical advice on how to vault it. I just haven't met any idiom like this before. Is it an actual phrase/idiom, or just _licentia poetica_? :) Full lyrics are here if you need more context.

I do not know this song, but from reading the lyrics, I agree that the (the vault used in gymnastics) is used metaphorically to refer to an obstacle. As far as I know, is not commonly used figuratively to mean obstacles, but lyrics are not restricted to use only established expressions. Moreover, if it were used literally, it would mean that the speaker specifies “behind the vault” as a meeting place, which sounds quite odd to me.