Target date's father with some angling gear, investing energy (8)
I believe the answer is:
deadline
'target date's' is the definition.
(date by which something must be done)
'father with some angling gear investing energy' is the wordplay.
'father' becomes 'dad' (informal term for father).
'with some angling gear' becomes 'line' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'investing' indicates putting letters inside (inserted letters are taken in or invested).
'energy' becomes 'e' (physics symbol as in E=mci).
'dad'+'line'='dadline'
'dadline' enclosing 'e' is 'DEADLINE'.
Can you help me to learn more?
(Other definitions for deadline that I've seen before include "Ideal end (anag)" , "Time by which task must be completed" , "Latest time for completion" , "Cut-off point" , "Time by which journalist must file copy" .)