Can boys just randomly get a semi-hardon with out anything turning them on?

More than semi: A good hard erection is common even in a boy who's years before puberty. Often the trigger is just thinking about how he'll be a grown man someday, like dad or his favorite athlete. During the teenaged years, this happens maybe a dozen times a day. There's nothing "spiritual" about worrying about or trying to suppress this gift, which will enable sharing of love and becoming a father himself.