box clever (British)

to behave in a clever and sometimes slightly dishonest way to try to achieve a result you want
Usage notes: A good boxer (= man who fights as a sport) is a person who uses skill as well as strength to win fights.
Obviously he would have to box clever in the witness stand to avoid implicating himself.
boxing clever - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.

Idiom Definitions for 'Box clever'
If you box clever, you use your intelligence to get what you want, even if you have to cheat a bit.