(Sha ni kamaeru; “take a diagonal stance”)
To behave as if the situation isn’t serious; to adopt a (mockingly) aloof attitude, especially toward an opponent or problem. To view things in an ironic or cynical light.
Technically this verb phrase, by virtue of having a verb, could serve as a complete sentence… it probably won’t, though.
We have a noun, 斜 (sha), “diagonal,” and a verb, 構える (kamaeru), “to set (something) up.” They’re connected by the locational/directional particle に (ni).
This idiom comes from kendo (Japanese swordplay), describing a stance in which the sword is held at a downward angle, below waist level. Unlike many stances, this makes it difficult both to threaten a quick and deadly strike against one’s opponent and to defend oneself readily. Thus, the implication is that one isn’t taking one’s opponent seriously as a threat.
(“Sha ni kamaete shinken shoubu wo shite kurenai aite wa sokkou de taoseru hodo no chikara wo motsu senshu de atta.”)
[“S/he was an athlete who was strong enough to immediately knock down any opponent who adopted a dismissive attitude instead of fighting seriously.”]