If the withdrawal method is used right, the male partner will succeed in pulling out before ejaculation, something which may not always even happen. But just because the man pulled out before climaxing does not mean that no sperm was expelled into the female partner's body. Personally, I am convinced that those who say the withdrawal method works for them probably say so because they have won the lottery of natural luck or were charting to avoid (see natural family planning) and in either case did not have intercourse during the woman's ovulation. I am sure there are men who will not release any sperm before they ejaculate.
But if you really want to prevent pregnancy, do you really want to take that chance? The withdrawal method has a much better chance of working if you use basal body temperature, cervical mucus, or ovulation tests (or even better, all three!) to be sure when you are ovulating. Then you can avoid intercourse altogether during that time, and you will have no need at all to use pull out during the luteal phase, because the chances of getting pregnant between the end of ovulation and the onset of your period are exactly zero.