Forbid to draw the line wrong (4,3)
I believe the answer is:
rule out
'forbid' is the definition.
(thesaurus)
'draw the line wrong' is the wordplay.
'draw the line' becomes 'rule' (I can't justify this - if you can you should give a lot more credence to this answer).
'wrong' becomes 'out' (eg a calculation might be 'out').
'rule'+'out'='RULE OUT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for rule out that I've seen before include "Dismiss from consideration" , "Exclude as irrelevant or inadmissible" , "Decide against" , "Exclude as a possibility" , "Eliminate from consideration - using drawing stick?" .)