SeriesClick fires when the chart's series is clicked.
NOTE: In order to postback to the server when user selects or deselects point/points the chart AutoPostBack property needs to be set to true.
This event can be used for server side operations when user clicks on the chart. It is much the same as OnSelectionChanged event except that it does not need selection to be enabled:

<shield:ShieldChart ID="ShieldChart1" runat="server" 
protected void ShieldChart1_SeriesClick(object sender, ChartSeriesClickEventArgs e)
    // Perform some operation

For more information see Drill-Down example.