Update post_content everytime a custom post is opened in backend

The content_edit_pre filter might be what you are looking for. This filters the content of a post before it’s retrieved and output in the editor.

So you might be able to do this:

function save_team( $content, $post_id ) {
    $team = get_post_meta ($post_id , 'hometeam', true);
    if( get_post_type( $post_id ) == "game" && get_post_status( $post_id ) == "draft" ){
       //code that modifies post_content here by adding $team at some point
       $my_post = array(
          'ID' => $post_id,
          'post_content' => $content,);
       wp_update_post( $my_post );
    }
}
add_filter( 'content_edit_pre', 'save_team', 10, 2 );

The post ID and content are passed to this filter, so there’s no need to use get_post(); here.

As a side note, you should not use ‘ and ’ as quotations. Use ' or " instead.