Form - PHP question

// EDIT THE 2 LINES BELOW AS REQUIRED

$email_to = "info@davisburg.ca";

$email_subject = "Davisburg Sports Registration";

function died($error) {

    // your error code can go here

    echo "We are very sorry, but there were error(s) found with the form you submitted. ";

    echo "These errors appear below.<br /><br />";

    echo $error."<br /><br />";

    echo "Please go back and fix these errors.<br /><br />";

    die();

}



// validation expected data exists

if(!isset($_POST['players_first_name']) ||

    !isset($_POST['players_last_name']) ||

    !isset($_POST['players_birth']) ||
    !isset($_POST['soccer']) ||
    !isset($_POST['tball']) ||
    !isset($_POST['soccer_tball']) ||
    !isset($_POST['baseball_tball']) ||
    !isset($_POST['baseball_rookie']) ||
    !isset($_POST['baseball_mosquito']) ||
    !isset($_POST['baseball_peewee']) ||
    !isset($_POST['baseball_bantam']) ||

    !isset($_POST['parentnames']) ||

    !isset($_POST['email']) ||
    !isset($_POST['telephone']) ||

    !isset($_POST['mother_cell']) ||
    !isset($_POST['father_cell']) ||
    !isset($_POST['t_shirt']) ||
    !isset($_POST['volunteer']) ||

    !isset($_POST['comments']) ||
    !isset($_POST['waivername']) ||
    !isset($_POST['waiveraddress']) ||
    !isset($_POST['waiverphone']) ||
    !isset($_POST['waiver']) ||
    !isset($_POST['waiverdate'])) {


    died('We are sorry, but there appears to be a problem with the form you submitted.');       

}




$email_from = $_POST['email']; // required




$error_message = "";

$email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';

$error_message .= 'Please fill in a valid email address.<br />';

died($error_message);

$email_message = "Form details below.\n\n";



function clean_string($string) {

  $bad = array("content-type","bcc:","to:","cc:","href");

  return str_replace($bad,"",$string);

}
$email_message .= "Players First Name: ".clean_string($players_first_name)."\n";
$email_message .= "Players Last Name: ".clean_string($players_last_name)."\n";
$email_message .= "Players Birthdate: ".clean_string($players_birth)."\n";
$email_message .= "Soccer: ".clean_string($soccer)."\n";


$email_message .= "Baseball: ".clean_string($baseball)."\n";

$email_message .= "Parent's Names: ".clean_string($parentnames)."\n";
$email_message .= "Home Telephone: ".clean_string($telephone)."\n";
$email_message .= "Mother's Cell: ".clean_string($mother_cell)."\n";
$email_message .= "Fathers's Cell: ".clean_string($father_cell)."\n";
$email_message .= "T-Shirt:".clean_string($t_shirt)."\n";

            $email_message .= "Volunteer: ".clean_string($volunteer)."\n";
            $email_message .= "Comments: ".clean_string($comments)."\n";
            $email_message .= "Waiver Name: ".clean_string($waivername)."\n";
            $email_message .= "Waive Address: ".clean_string($waiveraddress)."\n";
            $email_message .= "Waiver Phone: ".clean_string($waiverphone)."\n";
            $email_message .= "Waiver: ".clean_string($waiver)."\n";
            $email_message .= "Waiver Date: ".clean_string($waiverdate)."\n";