Observed college is backed by deputy head (5)
I believe the answer is:
noted
'observed' is the definition.
('note' can be a synonym of 'observe')
'college is backed by deputy head' is the wordplay.
'college' becomes 'eton' (I've seen this before).
'is backed' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'head' indicates taking the first letters.
The initial letter of 'deputy' is 'd'.
'eton' in reverse letter order is 'note'.
'note'+'d'='NOTED'
(Other definitions for noted that I've seen before include "Celebrated or recorded" , "Observed - recorded" , "Remarkable" , "written down" , "Having renown" .)