One potential science fair project is an experiment about how air pressure affects how high a basketball will bounce. The project will need a testable hypothesis.
There are many aspects of the game of basketball that can be examined through a scientific lens. A science fair project about air pressure, for example, could study the effects that more or less air pressure have on ball bounce height. The student could also test how different surfaces, such as asphalt vs. grass, or different drop heights, such as from a balcony vs. from a rooftop, affect bounce.
A science project must have a working hypothesis. A hypothesis is an educated guess. For example "A basketball will bounce higher on asphalt than on grass." The hypothesis must also be testable, meaning the student must have access to the equipment and terrain to carry out the experiment.
Another science fair project, studies how hand placement affects basketball shooting. The experiment measures what percentage of shots are successful when the player shoots them from chin-height, chest height, or above the head. The hypothesis could be "Starting position does not affect the player’s likelihood of shooting a basket." A hypothesis may be proven wrong during an experiment, but this is what makes a science project valuable and fun.
Other experiments could include the effect of a basketball’s rotation on the likelihood of making a shot, or how high or low altitude affects player performance or air pressure in a basketball.