Travelling salesman encountered getting up in a bad mood (6)
I believe the answer is:
temper
'a bad mood' is the definition.
(I've seen this before)
'travelling salesman encountered getting up' is the wordplay.
'travelling salesman' becomes 'rep' (I've seen this before).
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'getting up' says the letters should be written backwards.
'rep'+'met'='repmet'
'repmet' written backwards gives 'TEMPER'.
'in' is the link.
(Other definitions for temper that I've seen before include "Modify" , "bait" , "Mood (often bad)" , "(Calm or furious) disposition" , "Moderate - anger" .)