It's worse when the rope tangles round the back of tractor (6)
I believe the answer is:
poorer
'it's worse' is the definition.
(I've seen this in another clue)
'the rope tangles round the back of tractor' is the wordplay.
'tangles' indicates anagramming the letters (I've seen 'tangled' mean this).
'round' indicates putting letters inside.
'the back of tractor' becomes 'or' (I can't justify this - if you can you should give a lot more credence to this answer).
'rope' is an anagram of 'poer'.
'poer' going around 'or' is 'POORER'.
'when' is the link.
Can you help me to learn more?
(Other definitions for poorer that I've seen before include "Less well-off" , "'Having less money, fewer possessions (6)'" , "Less rich" , "More impecunious" .)