Amateur going into action is held up (7)
I believe the answer is:
delayed
'is held up' is the definition.
(similar in meaning)
'amateur going into action' is the wordplay.
'amateur' becomes 'lay' (similar in meaning).
'going into' indicates putting letters inside.
'action' becomes 'deed' (deed is a kind of action).
'lay' inserted into 'deed' is 'DELAYED'.
(Other definitions for delayed that I've seen before include "Shelved" , "Detained, help up" , "Hindered" , "Put back" , "Made late" .)