In arrears, it's a nuisance being interrupted with 'What?' (6)
I believe the answer is:
behind
'in arrears' is the definition.
(I've seen this in another clue)
'a nuisance being interrupted with what?' is the wordplay.
I cannot quite see how this works, but
'what?' could be 'eh' (sound used to ask 'what?' or 'pardon?') and 'eh' is located in the answer.
'nuisance' could be 'bind' (I've seen this before) and 'bind' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for behind that I've seen before include "Hidden by; bottom" , "Following - late" , "in van? No" , "Taking place in secret" , "Hidden by; in arrears" .)