Set static page as default front page on newly created sites in multisite

Try the following code. Based on these two Q&A’s (not tested):

• How to add Custom Blog Options to new blog setup form?

• Programmatically set page_on_front

add_action( 'wpmu_new_blog', 'process_extra_field_on_blog_signup', 10, 6 );

function process_extra_field_on_blog_signup( $blog_id, $user_id, $domain, $path, $site_id, $meta ) {
    switch_to_blog($blog_id);
    $homepage = get_page_by_title( 'Sample Page' );   
    if ( $homepage )
    {
        update_blog_option( $blog_id, 'page_on_front', $homepage->ID );
        update_blog_option( $blog_id, 'show_on_front', 'page' );
    }
    restore_current_blog();
}

Use it as a Must Use plugin.