Pitch declared first-class for part of match (6)
I believe the answer is:
chukka
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for chukka that I've seen before include "A period of play in horse polo" , "Division of a polo match" , "Period of play in a polo match" , "Polo game division" , "Period in polo or leather boot" .)