When someone writes a comment on your WordPress website, he can/is required to fill his Name (Required), Email (Required) and Website URL. If we remove the Website URL field from the WordPress comment form (using some PHP code), number of comments receiving to your blog can be dropped in a bad way. But adding the code given below into your functions.php file, WordPress comment authors names will be shown as plain text without linking to their websites.

function btt_remove_comment_author_link($output) {
	global $comment;
	
	$author = get_comment_author();
	
	if ((get_comment_type() == 'comment')) {
		if ($comment->user_id > 0 && $user = get_userdata($comment->user_id))
			return $output;
		else
			return $author;
	} else {
		return $output;
	}
}
add_filter('get_comment_author_link', 'btt_remove_comment_author_link');