while($rows = $result->fetch_assoc())[1]
    {
        print '<tr>
                   <td>'.$rows ['first_name'].'</td>
                   <td>'.$rows ['last_name'].'</td>
                   <td>'.$rows ['gender'].'</td>
                   <td>'.$rows ['nationality'].'</td>
                   <td>'.$rows ['countries'].'</td>
                   <td>'.$rows ['adress'].'</td>
                   <td>'.$rows ['passport'].'</td>
                   <td>'.$rows ['phone'].'</td>
                   <td>'.$rows ['date_birsd'].'</td>
                   <td><a href="del_sportsmans.php">Удалить</a></td>
         </tr>';
    }

'<td><a href="del_sportsmans.php?id='.$rows['id'].'">Удалить</a></td>'

$id = $_REQUEST['id'];

DELETE FROM <имя таблицы> WHERE <идентификатор>=$id