Flag down fellow crossing junction (4,5)
I believe the answer is:
blue peter
'flag' is the definition.
(blue peter is a kind of flag)
'down fellow crossing junction' is the wordplay.
I cannot really see how this works, but
'down' could be 'blue' (both can mean sad) and 'blue' is found within the answer.
'junction' could be 't' and 't' is found in the answer.
'fellow' could be 'peer' (both can mean an equal) and 'peer' is found in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for blue peter that I've seen before include "shown readiness to go overseas" , "Ship's flag on leaving port" , "Waver before leaving" , "BBC children's programme" , "Flag showing ship is about to leave" .)