Set a limit (4,3,4)
I believe the answer is:
draw the line
'set a limit' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for draw the line that I've seen before include "Set a limit on what's allowed" , "what an angler might do?" , "Find unacceptable - fix a limit" , "Set a limit on - reasonably object to" .)