Use the max_teams value to determine how many sp_teams can be added to a league (cpt)

limit-teams-per-league.php

<?php

// changing the league status
add_action('updated_post_meta', 'change_league_status', 0, 4);
function change_league_status($meta_id, $post_id, $meta_key, $meta_value) {

    $active_teams = get_post_meta( $post_id, 'active_teams' );    // getting active teams id's
    $max_teams = (int)get_post_meta( $post_id, 'max_teams' )[0];  // getting number of max teams
    $active_teams_length = count($active_teams);                  // getting active teams length
    if($active_teams_length === $max_teams){
        update_post_meta( $post_id, 'league_open', 'closed');     //converting league status
    }
    if($active_teams_length < $max_teams){
        update_post_meta( $post_id, 'league_open', 'open');       //converting league status
    }
    if($active_teams_length > $max_teams){
        $teams_differance = $active_teams_length-$max_teams;      //getting differance
        $reverse_array = array_reverse($active_teams);
        for ($i = 0; $i < $teams_differance ; $i++ ){             //deleting extra teams
            delete_post_meta( $post_id, 'active_teams', $reverse_array[$i] );
        }
        update_post_meta( $post_id, 'league_open', 'closed');     //converting league status
    }


}