Tank ending in ditch surrounded by rubbish (6)
I believe the answer is:
thrash
'tank' is the definition.
(defeat heavily - informal Scottish)
'ending in ditch surrounded by rubbish' is the wordplay.
'ending in' indicates one should take the final letters.
'surrounded by' is an insertion indicator.
'rubbish' becomes 'trash' (synonyms).
The last letter of 'ditch' is 'h'.
'h' put into 'trash' is 'THRASH'.
(Other definitions for thrash that I've seen before include "Trounce, beat soundly" , "Whip repeatedly" , "Best" , "Beat violently" , "Beat hard" .)