Final answer:
The best cross-sell item for someone purchasing a soccer ball would be a soccer jersey, as it is closely related to and used in the same sport.
Step-by-step explanation:
If a customer was about to purchase a soccer ball, the best item to try to cross-sell would be a soccer jersey. Cross-selling is a sales technique used to get a customer to spend more by purchasing a product that's related to what they're already buying. In this case, the soccer jersey is closely related to the soccer ball as they are both used in the same sport.
A soccer jersey would complement the soccer ball purchase and appeal to the customer's interest in the sport. It would also provide an opportunity for the customer to show support for their favorite soccer team while playing the sport.