Ran infidels off Holy Island (11)
I believe the answer is:
lindisfarne
'holy island' is the definition.
(I've seen this before)
'ran infidels off' is the wordplay.
'off' indicates anagramming the letters.
'ran'+'infidels'='raninfidels'
'raninfidels' with letters rearranged gives 'LINDISFARNE'.
(Other definitions for lindisfarne that I've seen before include "Holy Island" , "north-eastern island" , "peninsula?" .)