Preoccupation of guard after period of leave (7,2,4)
I believe the answer is:
absence of mind
'preoccupation' is the definition.
(thesaurus)
'of guard after period of leave' is the wordplay.
'guard' becomes 'mind' (both can mean to look after).
'after' is a charade indicator (letters next to each other).
'period of leave' becomes 'absence' (I can't explain this - if you can you should believe this answer much more).
'of'+'mind'='ofmind'
'ofmind' after 'absence' is 'ABSENCE OF MIND'.
Can you help me to learn more?
(Other definitions for absence of mind that I've seen before include "Proverbially professorial trait" , "Failure to remember what one is doing" .)