Eccentric person needing low dam to perform (6)
I believe the answer is:
weirdo
'eccentric person' is the definition.
(I've seen this before)
'low dam to perform' is the wordplay.
'low dam' becomes 'weir' (I've seen this before).
'to perform' becomes 'do' ('do' can be a synonym of 'perform').
'weir'+'do'='WEIRDO'
'needing' acts as a link.
(Other definitions for weirdo that I've seen before include "Person who behaves bizarrely" , "Bizarre character" , "Slang for odd or eccentric person" , "Odd fish" , "Informally, an eccentric or very strange person" .)