Asking for a friend. What if the baby doesn't deliver even though the mum is pushing hard?

My friend tried to push baby out for long time and gynae tried to pull the baby out but in no avail and emergency c-section was performed and found out baby's right arm was tangled by his umbilical cord. However, this might be one of the very rare cases baby not able to be pushed out due to umbilical cord. In normal case, doctor will use assisted birth instrument such as forceps or vacuum to get the baby out.