Undecided location of the broken line (6-2-3-4)
I believe the answer is:
middle-of-the-road
'undecided' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I can't see?
'location of the broken line' is the wordplay.
I cannot really understand how this works, but
'location' could be 'middle' (middle is a kind of location) and 'middle' is found within the answer.
'of' could be 'o' and 'o' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for middle-of-the-road that I've seen before include "place for dangerous drivers?" , "Unexciting" , "Avoiding extremes; moderate" , "Safe" , "Average" .)