An historic period back in sports ground? (5)
I believe the answer is:
arena
'sports ground?' is the definition.
(I've seen this before)
'an historic period back' is the wordplay.
'historic period' becomes 'era' (I've seen this before).
'back' says the letters should be written in reverse.
'an'+'era'='anera'
'anera' backwards is 'ARENA'.
'in' is the link.
(Other definitions for arena that I've seen before include "Amphitheatre's central space" , "Sporting enclosure" , "Sphere of intense activity" , "Sporting venue enclosed by seats" , "Area of endeavour" .)