Play baseball with frequency (5)
I believe the answer is:
pitch
'frequency' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pitch that I've seen before include "Throw - black stuff" , "Slope, of a roof say" , "waterproof coat" , "bowl" , "Playing field as for football" .)