Prevent posts from being published unless a taxonomy is selected

I’ve created a custom taxonomy in WordPress. I want to prevent posts from being published unless a taxonomy is selected. What hook do I need to use to do that? I want to use only php hooks, not jQuery.

Code to create the taxonomy:

function sport_type_st_t(){ 
    /*** =========== Sport type ================== ***/
    $argsT=array( 
         'labels'=>array( 'name'=>__('Sport Types'), 
                          'singular_name'=>__('Sport Type'), 
                          'all_items'=>__('All Sport Type'), 
                          'search_items'=>__('Search Sport Type'), 
                          'edit_item'=>__('Edit Sport Type'), 
                          'view_item'=>__('View Sport Type'), 
                          'update_item'=>__('Update Sport Type'), 
                          'add_new_item'=>__('Add Sport Type'), 
                          'new_item_name'=>__('New Sport Type'), ), 
                          'hierarchical' => true, 'public'=>true, ); 

    register_taxonomy( 'sport_type_st_t', array('post'), $argsT ); //add_filter( 'custom_menu_order', 'wpse_73006_submenu_order' ); 
    }

add_action('init','sport_type_st_t',20.1);