It upset socialist on loch showing fatigue (9)
I believe the answer is:
tiredness
'fatigue' is the definition.
(I know that fatigue can be written as tiredness)
'it upset socialist on loch' is the wordplay.
'upset' shows that the letters should be reversed in order.
'socialist' becomes 'red' (red can informally mean a socialist).
'on' says to put letters next to each other.
'loch' becomes 'ness' (Loch Ness in Scotland).
'it' reversed gives 'ti'.
'ti'+'red'+'ness'='TIREDNESS'
'showing' acts as a link.
(Other definitions for tiredness that I've seen before include "Residents in state of fatigue" , "7 (anag)" , "Weariness" , "Weary feeling" , "That's liable to occur at midnight" .)