Stop baseball team making comeback (4)
I believe the answer is:
stem
'stop' is the definition.
(stemming is a kind of stopping)
'baseball team making comeback' is the wordplay.
'baseball team' becomes 'Mets' (New York Mets).
'making comeback' says the letters should be written backwards.
'mets' in reverse letter order is 'STEM'.
(Other definitions for stem that I've seen before include "section of pipe" , "Originate (from)" , "Vertical part of flower or drinking glass" , "Flower's stick" , "Restrain - staunch - supporter" .)