Anal birth is when the baby/ies are delivered via the anus.
There are many given explanations for anal births. One such explanation, as fully explained here , gives a 1 in 20 billion chance of a male naturally conceiving, involving various birth defects that would either have a vagina behind his scrotum, or have a uterus, etc. connected to his anal passage.
Here is another article, proving the possiblity of anal delivery in females, and therefore possibly males.