Assign personal assistant upset by score (7)
I believe the answer is:
appoint
'assign' is the definition.
(assign can mean to appoint or delegate)
'personal assistant upset by score' is the wordplay.
'personal assistant' becomes 'PA' (abbreviation).
'upset' is a reversal indicator.
'by' means one lot of letters go next to another.
'score' becomes 'point' ().
'pa' written backwards gives 'ap'.
'ap'+'point'='APPOINT'
(Other definitions for appoint that I've seen before include "Choose for a job" , "Employ; take on" , "Pick" , "Assign job to (someone)" , "Assign to a duty" .)