Casual shoe’s telltale wear oddly ignored (7)
I believe the answer is:
sneaker
'casual shoe's' is the definition.
(I've seen this before)
'telltale wear oddly ignored' is the wordplay.
'telltale' becomes 'sneak' (I've seen this before).
'oddly ignored' means one should take alternating letters.
The alternating letters of 'wear' are 'er'.
'sneak'+'er'='SNEAKER'
(Other definitions for sneaker that I've seen before include "one tending to go unnoticed?" , "Trainer (shoe)" , "American trainer" , "Canvas shoe" , "Soft shoe" .)