Managed to control board game set up -- it's gnarly (7)
I believe the answer is:
nodular
'it's gnarly' is the definition.
(thesaurus)
'managed to control board game set up' is the wordplay.
'managed' becomes 'ran' (both can mean organised or was in charge of).
'to control' indicates putting letters inside.
'board game' becomes 'ludo' (ludo is a kind of board game).
'set up' says the letters should be written in reverse (in a down clue, letters go up).
'ran' going around 'ludo' is 'raludon'.
'raludon' backwards is 'NODULAR'.
(Other definitions for nodular that I've seen before include "Having tiny knots" , "Lumpy" , "Knobbly" , "Having small lumps" , "Relating to swellings" .)