Disappoint old and new sportsmen at the centre — sorry! (3,4)
I believe the answer is:
let down
'disappoint' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
(Other definitions for let down that I've seen before include "blow" , "Disappointment < lowered" , "deflating" , "Disappoint, fail to support" , "Failed - deflated" .)