Brainbox troubled by cracking ideas? (7)
I believe the answer is:
egghead
'brainbox' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for egghead that I've seen before include "Heed gag about slang intellectual" , "Intellectual - highbrow" , "scholar" , "Cracked" , "Brainiac" .)