Country bumpkin left, going after pair of oxen (5)
I believe the answer is:
yokel
'country bumpkin' is the definition.
(thesaurus)
'left going after pair of oxen' is the wordplay.
'left' becomes 'l' (common abbreviation).
'going after' says to put letters next to each other.
'pair of oxen' becomes 'yoke' (I've seen this before).
'l' put after 'yoke' is 'YOKEL'.
(Other definitions for yokel that I've seen before include "Hick" , "Simple rustic" , "Rustic - peasant" , "Unsophisticated country person" , "Unsophisticated rustic" .)