Making a little ballerina nervous is foolish (5)
I believe the answer is:
inane
'foolish' is the definition.
(inane can mean silly or foolish)
'making a little ballerina nervous is' is the wordplay.
'making a little' says the answer is hidden in the clue (the solution makes a little part of the clue).
'INANE' can be found hidden inside 'ballerina nervous is'.
(Other definitions for inane that I've seen before include "Lacking sense, silly" , "Foolish, fatuous" , "Empty" , "Really stupid" , "Devoid of intelligence" .)