The Ball’s in Your Court
This perfectly illustrates why English can be so perplexing for non-native speakers to learn. Many words have multiple meanings, and misunderstandings are bound to occur without explicit context. However, it’s heartwarming that she assured him it wouldn’t be an issue.
It’s also amusing that the guy even thought to give her a warning. I always assumed that tennis balls were fair game in this dog-eat-dog world. Whoever is the quickest claims the toy. Isn’t that how it works? I wouldn’t be upset with someone’s dog if they grabbed our tennis balls at the park.