[azzerking]

Holy Crap,

Your script is completely open to MySQL Injection.

Code:

$query = "SELECT Username, Password FROM `Users` WHERE `Username` = '".$_POST["playerName"]."'";
$result = mysqli_query($conn, $query);

Please use prepared statements.

Code:

$stmt = $mysqli->prepare("SELECT Username, Password FROM `Users` WHERE `Username` = :username ");
$stmt->execute( array( ":username", $_POST[ 'playerName' ] ) );

PHP Prepared Statements