Commotion at university about rider's first foot support (7)
I believe the answer is:
stirrup
'foot support' is the definition.
(I've seen this before)
'commotion at university about rider's first' is the wordplay.
'commotion' becomes 'stir' (stir can mean a commotion).
'at university' becomes 'up' (slang term meaning at university).
'about' is a charade indicator (letters next to each other).
'rider's first' becomes 'r' (1st letter of 'rider').
'up' after 'r' is 'rup'.
'stir'+'rup'='STIRRUP'
(Other definitions for stirrup that I've seen before include "Horse rider's footrest" , "Equestrian footrest" , "Rider's foot support" , "one puts the boot into" , "Foot support in riding" .)