But one day, Napoleon said that his rival Snowball was a spy of the farmers and chased him away.

chased 是动词 chase 的过去式，意思是"追赶、追逐"。 away 是副词，表示"离开、远离"的意思。 chased away 这个短语表示"赶走、驱逐"，指通过追赶或威胁使某人离开某个地方。