Restraint in allocation under way (10)
I believe the answer is:
moderation
'restraint' is the definition.
(I've seen this before)
'allocation under way' is the wordplay.
'allocation' becomes 'ration' (I've seen this before).
'under' is a charade indicator (letters next to each other).
'way' becomes 'mode' ('mode' can be a synonym of 'way').
'ration' after 'mode' is 'MODERATION'.
'in' acts as a link.
(Other definitions for moderation that I've seen before include "Avoidance of excess" , "Avoidance of extremes" , "restraint" , "avoids extremes" , "self-restraint" .)