Catch a girl - nothing to it (5)
I believe the answer is:
lasso
'catch' is the definition.
(I know that lasso is a type of catch)
'a girl nothing to it' is the wordplay.
'a girl' becomes 'lass' (lass can informally mean a girl).
'nothing' becomes 'O' (O resembles 0).
'to it' says to put letters next to each other.
'lass'+'o'='LASSO'
(Other definitions for lasso that I've seen before include "Rope for catching livestock" , "One may be caught by this" , "which may be catching" , "Cattle-catching rope" , "snare" .)