Half of team keen to bring in new youngster (8)
I believe the answer is:
teenager
'youngster' is the definition.
(thesaurus)
'half of team keen to bring in new' is the wordplay.
'half of' indicates taking half.
'keen' becomes 'eager' (I've seen this before**).
'to bring in' means one lot of letters goes inside another.
'new' becomes 'n'.
'team' halved is 'te'.
'eager' going around 'n' is 'enager'.
'te'+'enager'='TEENAGER'
(Other definitions for teenager that I've seen before include "hormonal problem?" , "14, perhaps" , "youth, perhaps" , "Generate (anag)" , "Youngster" .)