Peer taking part in the qualifier (5)
I believe the answer is:
equal
'peer' is the definition.
(I know that peer can be written as equal)
'part in the qualifier' is the wordplay.
'part in' says the answer is hidden in the clue.
'EQUAL' can be found hidden inside 'the qualifier'.
'taking' acts as a link.
(Other definitions for equal that I've seen before include "The same in all aspects" , "Evenly-matched" , "Keep pace with - peer" , "Peer; evenly balanced" , "Evenly matched" .)