A boy initially enthralled by east European entertainer (7)
I believe the answer is:
acrobat
'entertainer' is the definition.
(type of circus entertainer)
'a boy initially enthralled by east european' is the wordplay.
'initially' indicates taking the first letters.
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'east european' becomes 'Croat' (someone from Croatia).
The first letter of 'boy' is 'b'.
'b' placed into 'croat' is 'crobat'.
'a'+'crobat'='ACROBAT'
(Other definitions for acrobat that I've seen before include "Taco bar (anag.)" , "Circus entertainer" , "circus artiste" , "Athletic Circus Performer" , "Agile entertainer" .)