Not open to accommodate top new athletics event (4,3)
I believe the answer is:
shot put
'athletics event' is the definition.
'not open to accommodate top new' is the wordplay.
'not open' becomes 'shut' ('shut' is the opposite to 'open').
'to accommodate' is an insertion indicator.
'new' is an anagram indicator.
'top' with letters rearranged gives 'otp'.
'shut' going around 'otp' is 'SHOT-PUT'.
(Other definitions for shot put that I've seen before include "Competition in which a heavy metal ball is hurled" , "Throwing contest" , "Athletic field event" , "Throwing event" , "Olympic event" .)