Fool about whilst playing electronic instrument (3,7)
I believe the answer is:
tin whistle
'instrument' is the definition.
(tin whistle is a kind of instrument)
'fool about whilst playing electronic' is the wordplay.
'fool' becomes 'nit' (both can mean a stupid person).
'about' says the letters should be written backwards.
'playing' indicates an anagram.
'electronic' becomes 'e' (as in e-mail or e-books).
'nit' reversed gives 'tin'.
'whilst' with letters rearranged gives 'whistl'.
'tin'+'whistl'+'e'='TIN WHISTLE'
(Another definition for tin whistle that I've seen is " Cheap, six-holed metal flageolet".)