Obstruction, wide, first to last leading to jam (9)
I believe the answer is:
roadblock
'obstruction' is the definition.
(I know that roadblock is a type of obstruction)
'first to last leading to jam' is the wordplay.
'first' is a charade indicator (letters next to each other).
'to last leading' becomes 'road' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to jam' becomes 'block' ('block' can be a synonym of 'jam').
'road' next to 'block' is 'ROADBLOCK'.
'wide' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for roadblock that I've seen before include "Barrier to traffic" , "Paving stone" , "Barrier constructed by police" , "Police barricade to halt traffic" , "Traffic-halting barrier" .)