<asp:DropDownList id="ddlFoo" runat="server">
    ...
</asp:DropDownList>
<asp:TextBox id="txtBar" runat="server" Text='<%# ddlFoo.SelectedValue %>' />

<%-- For query string --%>
<asp:TextBox id="txtBar" runat="server"
    Text='<%# Request.QueryString["Key_Value"] %>' />

<uc1:CompetitionClassification ID="CompetitionClassification" runat="server" OnlyTopFive="True" />

private bool onlyTopFive;
  public bool OnlyTopFive
    {
        get
        {
            return this.onlyTopFive;
        }
        set
        {
            this.onlyTopFive = value;
        }
    }