Stitches on a baseball (4)
I believe the answer is:
seam
'stitches on a baseball' 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 "Join in material - layer of coal" , "Line of join" , "Join - stratum of ore" , "A stitched join in a garment" , "Join round cricket ball" .)