Small ambition limits innocent person (4)
I believe the answer is:
lamb
'innocent person' is the definition.
(I've seen this in other clues)
'small ambition limits' is the wordplay.
'limits' indicates a hidden word (the answer is surrounded or limited by the clue).
'LAMB' can be found hidden inside 'small ambition'.
(Other definitions for lamb that I've seen before include "Tender sheep meat" , "Agnus Dei - . . . . of God" , "Meaty" , "Young farm animal" , "English essayist" .)