Trouble in Wag group (5)
I believe the answer is:
aggro
'trouble' is the definition.
(short for aggression or aggravation)
'in wag group' is the wordplay.
'in' says the answer is hidden in the clue.
'AGGRO' is hidden in the letters of 'wag group'.
(Other definitions for aggro that I've seen before include "Difficulties (informal)" , "offensive behaviour" , "Aggressive, violent behaviour in short" , "Problems and difficulties" , "Bovver!" .)