Briefly stay with baseball player (9)
I believe the answer is:
shortstop
'baseball player' is the definition.
(shortstop is a kind of baseball player)
'briefly stay' is the wordplay.
'briefly' becomes 'short' (I can't justify this - if you can you should believe this answer much more).
'stay' becomes 'stop' (stop is a kind of stay).
'short'+'stop'='SHORTSTOP'
'with' is the link.
Can you help me to learn more?
(Other definitions for shortstop that I've seen before include "Baseball player" , "US player" , "One in field" , "Fielding position (baseball)" , "position in American sport" .)