On balance, not so unable to stay still (8)
I believe the answer is:
restless
'unable to stay still' is the definition.
I can't tell whether this defines the answer.
'on balance not' is the wordplay.
'on' says to put letters next to each other.
'balance' becomes 'rest' (I've seen this before).
'not' becomes 'less' (I've seen this in other clues).
'rest'+'less' is 'RESTLESS'.
'so' is the link.
Can you help me to learn more?
(Other definitions for restless that I've seen before include "Unsettled, fidgety" , "Constantly active" , "Worried and uneasy" , "Uneasy and agitated" , "Wakeful" .)