At some stage, a novice will fall behind (3)
I believe the answer is:
lag
'fall behind' is the definition.
('lag' can be a synonym of 'fall behind')
'at some stage a novice will' is the wordplay.
'at' means one lot of letters go next to another.
'some stage' indicates an anagram (I've seen 'staged' mean this ('staged' can mean 'organised')).
'novice' becomes 'l' (abbreviation for Learner e.g. on UK cars).
'will' becomes 'g' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'l'='al'
'al' anagrammed gives 'la'.
'la' put next to 'g' is 'LAG'.
Can you help me to learn more?
(Other definitions for lag that I've seen before include "Fall behind or cover to prevent heat loss" , "Protect from cold" , "Drag one's feet" , "Cover pipes" , "Ex-convict" .)