Pressure on amateur to perform (4)
I believe the answer is:
play
'perform' is the definition.
(playing is a kind of performing)
'pressure on amateur' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'on' says to put letters next to each other.
'amateur' becomes 'lay' ('lay' can be similar in meaning to 'amateur').
'p'+'lay'='PLAY'
'to' acts as a link.
(Other definitions for play that I've seen before include "Portray in a drama" , "Theatre production" , "Participate in games or sport" , "Make sport" , "Perform music" .)