As he took his chainsaw to a leylandii tree, he hit the exact spot where a ball was embedded in the wood and sliced through it.
The ball apparently lodged in a fork of the tree many years ago when a golfer hooked a drive on the first tee. The conifer grew around the ball and it remained hidden in the screen of 15 trees.
Trimmed, sanded and varnished, it is to become a rather unusual trophy board at Eaton Golf Club in Norwich.
Mr Mitchell discovered the ball last month after he felled the 40ft trees, planted 37 years ago, and began cutting the timber into 4ft lengths for firewood.
The piece of wood with the half ball visible is being preserved and varnished by former club captain Jim Cook who is a skilled woodworker.
It will then be kept behind the bar and used to record the names of everyone who gets a hole-in-one on the 198-yard ninth hole.
Peter Johns, the manager of the £675-a-year club, said: 'It is just an incredible find.
'We think it came off the first tee. It must have lodged in a fork or embedded itself in the trunk and the tree grew round it.
'If Richard had cut the trunk an inch or two either way we'd never have known it was there.'
