When installing a basketball goal in your yard I would dig the hole to at least 2 feet deep and make the hole wide than the pole.
Then pour in some concrete and check to make sure the basketball pole is level before the concrete dries out.
The concrete should be fully set within 24 hours which is the minimum time you should wait before using the basketball goal.
When I installed my basketball goal I buried the pole to the basketball goal to 2 feet deep and it worked just fine.
When installing a basketball goal pole in the ground it's recommended to have at least 1/4 of the poles length in the ground.
As long as you bury the basketball goal pole in the ground to at least 15 inches to 2 feet with concrete then you should be okay.