Hide allow trackbacks/pingbacks

Under the discussion tab on the post page, there’s ‘allow comments’ and ‘allow trackbacks and pingbacks’, how would I hide the option to allow pingbacks from users but still have it be on by default?

Method 1 (CSS)

You can hide it for all non-admins via CSS:

function hide_ping_track_wpse_103502() {
    if( get_post_type() === "post" ){
        if( ! current_user_can( 'manage_options' ) ){
            // only for non-admins
            echo "<style>.meta-options label[for=ping_status], #ping_status{display:none !important;} </style>";
        }
    }
}
add_action( 'admin_head-post.php', 'hide_ping_track_wpse_103502' );

Before:

After:

Method 2 (PHP)

You can also remove the native discussion metabox and replace it with your own:

add_action( 'admin_menu', 'remove_discussion_meta_box' );
add_action( 'add_meta_boxes', 'add_custom_discussion_meta_box' );

function remove_discussion_meta_box() {
    remove_meta_box('commentstatusdiv', 'post', 'normal');
}

function add_custom_discussion_meta_box() {
        add_meta_box(
            'custom_discussion',
            __( 'Custom Discussion' ),
            'custom_discussion_meta_box',
            'post'
        );
}

function custom_discussion_meta_box($post) {
?>
<input name="advanced_view" type="hidden" value="1" />
<p class="meta-options">
        <label for="comment_status" class="selectit">
            <input name="comment_status" type="checkbox" id="comment_status" 
                   value="open" <?php checked($post->comment_status, 'open'); ?> /> 
            <?php _e( 'Allow comments.' ) ?>
        </label>

         <input name="ping_status" type="hidden" id="ping_status" 
                    value="<?php echo $post->ping_status;?>" />

        <?php do_action('post_comment_status_meta_box-options', $post); ?>
</p>
<?php
}

where the ping_status form input field is hidden with the current value.

After: