After endless hassle the night before, one enters in distress (8)
I believe the answer is:
aggrieve
'distress' is the definition.
(I've seen this before)
'after endless hassle the night before' is the wordplay.
'after endless hassle' becomes 'aggri' (I can't justify this - if you can you should give a lot more credence to this answer).
'the night before' becomes 'eve' (eve can mean the night before something).
'aggri'+'eve'='AGGRIEVE'
'one enters in' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for aggrieve that I've seen before include "Do an injustice to" , "Distress, afflict" , "Pain or injure" , "upset" , "Break the heart" .)