You need to modify the query for that. You have not included the
clause in the query. The query would look like
SELECT full_name FROM Players WHERE id = @id
and you need to add a SqlParameter to your code like
cmd.Parameters.Add(new SqlParameter("@id", DropDownList1.SelectedValue));
Of course, the parameters in the where query could vary depending upon the table structure in your case.
If you can provide it, I can help you further.