Baseball feature (4)
I believe the answer is:
seam
'baseball feature' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seam that I've seen before include "A layer of coal in ground" , "Stratum (of a mineral)" , "Underground layer of mineral" , "Stitched joint" , "Join - stratum of ore" .)