Will the amount of air in a basketball affect shooting shooting percentages?
If the amount of air in a basketball is outside a fairly small range, it will reduce the shooting percentages, all other things being equal.
If a ball is pumped up to an excessive pressure, shots that hit the rim will bounce more violently. This will make a shooter less likely to get the "shooter's roll." If the ball is too flat, it will not bounce much at all when it hits the rim. Shots will not, for example, hit the front of the rim and bounce up and over. Instead, they'll hit the front of the rim, flatten out, and fall to the floor.
Balls that are pumped up too much or not enough will yield lower shooting percentages than properly inflated balls.