Who claimed that they grappled? Rather, it is that they were moving around a lot in the womb (Genesis 25), and this raised questions that led to prophecy about them.
The text says:
After this, his brother came out, with his hand grasping Esau’s heel; so he was named Jacob.[c] Isaac was sixty years old when Rebekah gave birth to them.
I’m curuious what @deuteroKJ says, but that is sufficient ambiguous to not necessarily mean that Jacob was delivered with his arm extended and grasping Esau.
Regardless, it is possible for a baby to present an arm first. It is very dangerous, because it often leads to the baby getting stuck, which is a medical emergency. Still, it is possible to deliver a baby like this. Though, I doubt that arm is grasping the heal of the other baby while the delivery is happening.