Easy trip ruined by roughness (8)
I believe the answer is:
asperity
'roughness' is the definition.
(I've seen this before)
'easy trip ruined' is the wordplay.
'ruined' indicates an anagram.
'easy'+'trip'='easytrip'
'easytrip' anagrammed gives 'ASPERITY'.
'by' is the link.
(Other definitions for asperity that I've seen before include "Roughness, harshness or coldness" , "Harshness or severity of manner" , "rough manner" , "Harshness, bitter coldness" , "Roughness of temper" .)