Dwarf on BA is spoiled (6)
I believe the answer is:
bonsai
'dwarf' is the definition.
(I've seen this before)
'on ba is spoiled' is the wordplay.
'spoiled' indicates anagramming the letters.
'on'+'ba'+'is'='onbais'
'onbais' is an anagram of 'BONSAI'.
(Other definitions for bonsai that I've seen before include "Potted tree or shrub artificially prevented from reaching normal size" , "Art of growing dwarf varieties of tree" , "small growth" , "Japanese plant or tree grown in miniature form" , "Dwarf tree found in Bosnia" .)