Can I hit my head with a soccer ball ( during a match) 45 days after a FUE?

If the injury was severe enough to cause normal hair loss then it may affect your transplanted hairs.

At this point the grafts are completely incorporated into the scalp and you can do anything that you would have done had you not had a procedure.That includes heading a soccer ball!

As long as the area does not bleed from the hit or get burned ,than you won't cause a trauma. the first 10 days are the most critical time zone for a hair transplant operation.