Clumsy pioneer regularly taking part (5)
I believe the answer is:
inept
'clumsy' is the definition.
('inept' can be a synonym of 'clumsy')
'pioneer regularly taking part' is the wordplay.
'regularly taking' means one should take alternating letters.
'part' becomes 'pt' (I've seen this in other clues).
The alternate letters of 'pioneer' are 'ine'.
'ine'+'pt'='INEPT'
(Other definitions for inept that I've seen before include "Futile" , "Cack-handed" , "Showing a lack of competence" , "Awkward, clumsy" , "Lousy" .)