Nabs (7)
'nabs' is the definition.
('arrest' can be a synonym of 'nab')
This is the entire clue.
(Other definitions for arrests that I've seen before include "Apprehends" , "Stops and takes into custody" , "Checks" , "made by police" , "has a heart attack" .)
(Other definitions for catches that I've seen before include "Hidden drawbacks" , "Snags; door-fastenings" , "Drawbacks, difficulties not readily evident" .)