That's a big one.
I doubt however if this is really a throwing stick. A huge ball wouldn't 'fly' very far when thrown. It could be some kind of ceremonial piece, or...perhaps just a knobkerrie for a very big and strong man.
Is it made from one piece of wood ?
I have a club in my collection which has a hardwood ball and a very flexible handle. The seller told me that the handle was expendable. When it was broken, the owner just cut a new one. The head of the club, however, was used again.
It's from the Agoni-tribe in Swaziland and it is called 'chibonga'.
Total length : 67,5 cm
The second picture cleary shows that the handle is a separate piece of wood.
It's not easy to find examples of African throwing sticks in a book. Most books on African weapons only deal with iron weapons.
Nevertheless, here's one :
I have one stick in my collection which also could be a throwing club. I found this one in a shop in Brussels, filled with African goodies
I don't know anything about it. I showed it to a German friend and he also said in was used for throwing.
Length : 78,5 cm
Your club could also originate from the South Sea, for example Fiji. They also have throwing clubs.
So you see....perhaps more questions than answers