It’s shrewd to shout about being behind (6)
I believe the answer is:
crafty
'it's shrewd' is the definition.
(thesaurus)
'shout about being behind' is the wordplay.
'shout' becomes 'cry' ('cry' can be a synonym of 'shout').
'about' is an insertion indicator.
'being behind' becomes 'aft' (I've seen this before**).
'cry' enclosing 'aft' is 'CRAFTY'.
'to' is the link.
(Other definitions for crafty that I've seen before include "Cunning and artful" , "fly?" , "Cunning and ingenious" , "Cunning, deceitful" , "Guileful" .)