Disappointed by those when failed to keep up? (3,4)
I believe the answer is:
let down
'disappointed' is the definition.
(I've seen this before)
'those when failed to keep up?' is the wordplay.
I cannot really understand how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'keep' could be 'own' (keep can mean to own or possess) and 'own' is found within the answer.
The remaining letters 'ltd' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'by' is the link.
Can you help me to learn more?
(Other definitions for let down that I've seen before include "Failed - deflated" , "Aircraft descent" , "Disappointment < lowered" , "Failed - to deflate a tyre - disappointed" , "Lower" .)