Exclude script from all posts in a certain category…

Ok, so I’ve been looking & still haven’t come up with a solution.
Anyone?

So, what I’m trying to do here is enqueue an external script on every page in a site – except – posts in the ‘newsletters’ category.
The following works with regards to enqueueing the script – but not in excluding the script for all posts in the ‘newsletters’ category.
Help.
Please…

function my_custom_script() {

    if ( !is_admin() ) {

        /* Enqueue Scripts */
        wp_register_script('autoplay', ('my script goes here')); //first register your custom script
        wp_enqueue_script('autoplay'); // then let wp insert it for you or just delete this and add it directly to your template
    }
    elseif ($category != 'portfolio') {
        wp_deregister_script('autoplay');
    }
}
add_action( 'wp_print_scripts', 'my_custom_script'); // now just run the function