Some current knocked heater out of arena (12)
I believe the answer is:
amphitheatre
'arena' is the definition.
(I know that amphitheatre is a type of arena)
'some current knocked heater out' is the wordplay.
'some current' becomes 'amp' (unit of electrical current).
'knocked' becomes 'hit' (I've seen this in other clues).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'heater' with letters rearranged gives 'heatre'.
'amp'+'hit'+'heatre'='AMPHITHEATRE'
'of' is the link.
(Other definitions for amphitheatre that I've seen before include "Classical home for drama" , "Classical performance area" , "Roman tiered arena" , "Large oval stadium with tiers of seats" , "Arena; gallery tier" .)