Jack will be a breeder (5)
I believe the answer is:
raise
'jack' is the definition.
(I've seen this before)
'a breeder' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
The remaining letters 'rise' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'will be' is the link.
Can you help me to learn more?
(Other definitions for raise that I've seen before include "Bring up; levy" , "Bring up, rear" , "Wage increase" , "Care for during childhood" , "Call up" .)