var sel = $('.cmb2_select'),
    opt = $('option:not(:first-child)', sel);

function review(){
    var chosen = sel.map(function(i, el){
        return $(':selected',el);
    });
    var teamId = 0;
    opt.show();
    chosen.each(function(i, el){
        teamId = $(el).val();
        opt.not(el).filter(function(){
            return $(this).val() == teamId;
        }).hide();
    });
    return false;
}
sel.on('change',review);