You are using mysqli_query for multi query. so you have to use mysqli_multi_query.
change your code to:
<?php
$con=mysqli_connect("","","","");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$query="SET @rownum := 0;
INSERT INTO team( TeamRank, TeamName)
SELECT @rownum := @rownum + 1 AS TeamRank, TeamName
FROM (SELECT SUM(TeamRank)AS TeamRank , TeamName
FROM team
GROUP BY TeamName
ORDER BY TeamRank DESC) as result
ON DUPLICATE KEY UPDATE TeamName = VALUES(TeamName);
";
echo "<table border='1'>
<tr>
<th>Rank</th>
<th>TeamID</th>
<th>TeamName</th>
<th>Total Points</th>
</tr>";
if (mysqli_multi_query($con,$query)) {
do {
/* store first result set */
if ($result = mysqli_store_result($con)) {
while ($row = mysqli_fetch_row($result)) {
echo "<tr>";
echo "<td>" . $row['TeamRank'] . "</td>";
echo "<td>" . $row['TeamID'] . "</td>";
echo "<td>" . $row['TeamName'] . "</td>";
echo "<td>" . $row['TeamPoints'] . "</td>";
echo "</tr>";
}
mysqli_free_result($result);
}
} while (mysqli_next_result($con));
}
echo "</table>";
mysqli_close($con);
?>