I'm not sure what you're asking. Without an erection, it's unlikely that a man will have a full-blown climax, but he can still be leaking semen, which contains sperm (thousands per drop!), with only a partial erection. Also, that same leaking semen can contain bacteria or a virus that can give you many kinds of STD's.
Men can also fail to ejaculate with a complete erection, but will still be leaking pre-ejaculate.
I have hit the right spot by accident near my prostate gland & ejaculated twice without erection or major orgasm, so it can happen... But you need to be a little more specific to what you are getting at with your question.
Men can also fail to ejaculate with a complete erection, but will still be leaking pre-ejaculate.
Stephen