Though the Amorites were a specific group of people (Genesis 10:16), here it refers to the people living in Canaan before the Israelites.
When zeal (strong devotion or passion) is directed in the right way, it is commendable. The Bible gives positive examples of this kind of zeal (Numbers 25:11; 1 Kings 19:10). Saul’s zeal, however, was misdirected. He showed clear disregard for Israel’s covenant (a binding agreement) with the Gibeonites.