Tennis is a sport usually played between two players (singles) or between two teams of two players each (doubles). Each player uses a racquet that is strung to strike a hollow rubber ball covered with felt over a net into the opponent's court.
The modern game of tennis originated in the United Kingdom in the late 19th century as "lawn tennis" which has heavy connections to various field/lawn games as well as to the ancient game of real tennis. After its creation, tennis spread throughout the upper-class English-speaking population before spreading around the world.
The sport of modern tennis was brought to 17th century Europe along with Grantville. William Cavendish saw the sport being played by members of the Barbie Consortium and noted the similarity to Royal Tennis. William and the Consortium talked about royal and modern tennis.
One issue with playing modern tennis in the 17th century is that modern tennis balls are filled with pressurized air. They start to lose their bounce as soon as they are removed from their sealed can, and have a limited lifespan even if they are left in the can. By August of 1633, it was starting to get hard to find balls that were bouncy enough for modern tennis.