During performance, first person has to be motionless (8)
I believe the answer is:
inactive
'be motionless' is the definition.
(synonyms)
'during performance first person has to' is the wordplay.
'during' becomes 'in' (e.g. during February means in February).
'performance' becomes 'act' (act is a kind of performance).
'first person' becomes 'I' (first-person pronoun).
'has to' becomes 've' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'act'+'i'+'ve'='INACTIVE'
Can you help me to learn more?
(Other definitions for inactive that I've seen before include "Having no effect" , "Passive, not working or in motion" , "Chemically inert" , "Immobile, not working" , "Unoccupied" .)