Barrier caused by unusually drab old rugby player (9)
I believe the answer is:
roadblock
'barrier' is the definition.
(roadblock is a kind of barrier)
'unusually drab old rugby player' is the wordplay.
'unusually' is an anagram indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'rugby player' becomes 'lock' (second row of a scrum).
'drab'+'o'='drabo'
'drabo' anagrammed gives 'roadb'.
'roadb'+'lock'='ROADBLOCK'
'caused by' is the link.
(Other definitions for roadblock that I've seen before include "Checkpoint" , "Police barricade to halt traffic" , "Paving stone" , "Barrier constructed by police" , "Barrier on way" .)