Check if baseball team turned up (4)
I believe the answer is:
stem
'check' is the definition.
(thesaurus)
'baseball team turned up' is the wordplay.
'baseball team' becomes 'mets' (New York Mets).
'turned up' says the letters should be written in reverse.
'mets' back-to-front is 'STEM'.
'if' acts as a link.
(Other definitions for stem that I've seen before include "Axis" , "Thwart; support" , "It supports a plant" , "Slender upright part of wine glass" , "Stanch" .)