Pitcher's bagful (5)
I believe the answer is:
rosin
'pitcher's bagful' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rosin that I've seen before include "It's put on bow" , "It's used on a violin bow" , "Wax for violin bow etc." , "Colophony" , "Violin bow treatment" .)