Catch a girl with nothing on (5)
I believe the answer is:
lasso
'catch' is the definition.
(I know that lasso is a type of catch)
'a girl with nothing on' is the wordplay.
'a girl' becomes 'lass' (lass can informally mean a girl).
'with' means one lot of letters go next to another.
'nothing on' becomes 'o' (I've seen this in other clues).
'lass'+'o'='LASSO'
(Other definitions for lasso that I've seen before include "A cowboy's looped lariat" , "Catch (steers) with a rope" , "Ling-nosed rope" , "Rope used for catching cattle" , "Cow catcher" .)