Clear evidence of leg injury I had (6)
I believe the answer is:
limpid
'clear' is the definition.
(similar in meaning)
'evidence of leg injury i had' is the wordplay.
'evidence of leg injury' becomes 'limp' (someone with an injured leg might limp).
'i had' becomes 'I'd' (I'd).
'limp'+'id'='LIMPID'
(Other definitions for limpid that I've seen before include "Clear (writing, water)" , "Crystal clear, transparent" , "Clear, like air or water, say?" , "Crystal clear like pure water" , "Completely clear" .)