To exclude a novice is commonplace (5)
I believe the answer is:
banal
'commonplace' is the definition.
(I know that commonplace can be written as banal)
'to exclude a novice' is the wordplay.
'to exclude' becomes 'ban' (I've seen this in another clue).
'novice' becomes 'L' (as in a learner driver with L-plates on their car).
'ban'+'a'+'l'='BANAL'
'is' is the link.
(Other definitions for banal that I've seen before include "Pedestrian" , "Mundane" , "Trite or fatuous" , "Trite and insipid" , "Obvious and boring" .)