One's personal objective, though not a good score (3,4)
I believe the answer is:
own goal
'score' is the definition.
(I know that own goal is a type of goal)
'one's personal objective though not a good' is the wordplay.
I cannot quite see how this works, but
'personal' could be 'own' (eg one's own possessions are personal possessions) and 'own' is found within the answer.
'objective' could be 'goal' (goal can mean an objective or purpose) and 'goal' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for own goal that I've seen before include "move that backfired?" , "Self-inflicted problem" , "action that backfired?" , "Blunder penalising the perpetrator" , "Disadvantageous move for the party making it" .)