Excessive enthusiasm shown by some Tasmanians (5)
I believe the answer is:
mania
'excessive enthusiasm' is the definition.
(I've seen this in another clue)
'shown by some tasmanians' is the wordplay.
'shown by' indicates the answer is hidden within the clue.
'MANIA' is hidden within 'some tasmanians'.
(Other definitions for mania that I've seen before include "Insanity" , "Obsessive enthusiasm" , "fixation" , "Passion -- mood disorder" , "A (violent) mood disorder" .)