Vessel for baseball player (7)
I believe the answer is:
pitcher
This clue is a double definition.
'vessel' is the first definition.
(I know that pitcher is a type of jar)
'for baseball player' is the second definition.
(pitcher is a kind of baseball player)
(Other definitions for pitcher that I've seen before include "one tries to sell in a market?" , "One throwing" , "Baseball bowler and vessel for liquid" , "source of drink?" , "Earthenware vessel" .)