Pater, alas, coming to grief in gymnasium (9)
I believe the answer is:
palaestra
'gymnasium' is the definition.
(I've seen this before)
'pater alas coming to grief' is the wordplay.
'coming to grief' is an anagram indicator.
'pater'+'alas'='pateralas'
'pateralas' is an anagram of 'PALAESTRA'.
'in' acts as a link.
(Other definitions for palaestra that I've seen before include "Greek training school" , "In old athletics arena" , "gymnasium" .)