When I have open ended projects like this I just make up a fun story about the company, etc. It's asking you to be creative and use all of the principles of stats you have encountered to figure out how to test the tennis raquets serve "returnability".
I think the best thing to do would be for you to start writing up a proposal for an experiment and post it on here. Then we can guide you if we think your experiment needs some tweaking or if you are on the right track. There is no specific correct way to do it..you just need to be creative!