David asked the Gibeonites what they wanted done since Saul broke a covenant that Joshua and the elders had made with them by killing some of the Gibeonites. They said that they wanted seven male descendants to hang before the Lord in Gibeah of Saul.

The Bible reports that David did what they said, for he had said that he would do whatever they wanted that the famine might cease, for the Lord had brought a famine on Israel because of Saul’s sin.

…and [David] delivered them into the hands of the Gibeonites, and they hanged them on the hill before the LORD. So they fell, all seven together, and were put to death in the days of harvest, in the first days, in the beginning of barley harvest (2 Samuel 21.9). 

Saul had zeal, but not according to knowledge, and if it was according to knowledge, he let his zeal turn into rage, and he sinned.