Understand snag in operation (5,2)
I believe the answer is:
catch on
'understand' is the definition.
(thesaurus)
'snag in operation' is the wordplay.
'snag' becomes 'catch' (I've seen this before).
'in operation' becomes 'on'.
'catch'+'on'='CATCH ON'
(Other definitions for catch on that I've seen before include "twig" , "Get it" , "Understand - become fashionable" , "Informally, become popular or come to understand" .)