On about centre detective being upright (5)
I believe the answer is:
erect
'being upright' is the definition.
('erect' can be similar in meaning to 'upright')
'on about centre detective' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'about' shows that the letters should be reversed in order.
'centre' means to look at the middle letters.
The middle of 'detective' is 'ect'.
're' back-to-front is 'er'.
'er'+'ect'='ERECT'
(Other definitions for erect that I've seen before include "Found" , "Construct, build" , "Not having a list" , "Crete (anag)" , "Upright or vertical" .)