For his transgression - Compare 1 Chronicles 9:1. The “transgression” intended is probably the disobedience with respect to Amalek, recorded in 1 Samuel 15:1-9 (compare 1 Samuel 28:17-18).
Related Commentaries of 1 Chronicles 10:13
1 Chronicles 10:13
13 So Saul died for his transgression which he committede against the LORD, even against the word of the LORD, which he kept not, and also for asking counsel of one that had a familiar spirit, to enquire of it;