Hollywood actor's name in school plays (9)
'hollywood actor's' is the definition.
(actor Jack Nicholson)
'name in school plays' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'plays' indicates an anagram.
'inschool' with letters rearranged gives 'icholson'.
(Other definitions for nicholson that I've seen before include "Oscar winner 33", "See 8", "Jack -, US actor".)