Unusual kind of eccentric fraud (10,5)
I believe the answer is:
confidence trick
'fraud' is the definition.
(I've seen this before)
'unusual kind of eccentric' is the wordplay.
'unusual' is an anagram indicator.
'kind'+'of'+'eccentric'='kindofeccentric'
'kindofeccentric' is an anagram of 'CONFIDENCE TRICK'.
(Other definitions for confidence trick that I've seen before include "Deception" , "sting" , "scam" , "fraud" .)