I need to delete the inserted row in relationship grid event-Oninsertrow.
If you want to check some property before inserting row, you can try using onBeforeNew event in Relationship Item type.
In Part BOM item type I added below method in onBeforeNew client event. Similarly you can get the properties of relationship item and validate in onBeforeNew event.
var pState = aras.getItemProperty(parent.item,"state");
if(pState === "In Review")
alert("Part State is in In Review State. Cannot add new Relationship");