Ballplayer's hat (3)
I believe the answer is:
cap
'ballplayer's hat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cap that I've seen before include "Flat brimless hat" , "Dental work" , "'If the . . . fits, wear it' (3" , "Better; hat" , "Soft hat; crown" .)