Stop baseball team returning (4)
I believe the answer is:
stem
'stop' is the definition.
(stem can mean to stop or interrupt)
'baseball team returning' is the wordplay.
'baseball team' becomes 'mets' (New York Mets).
'returning' says the letters should be written in reverse.
'mets' in reverse letter order is 'STEM'.
(Other definitions for stem that I've seen before include "Stop the flow of, check" , "Basic skiing turn" , "Supporting structure" , "Block" , "Thwart; support" .)