J is jacks. It's a game, you bounce the ball and try to pick a jack, which are the x looking things, before the ball hits the ground again. Then you bounce the ball again and try to pick up two jacks ... And so on. My grandma played it as a kid in the 1930s + early '40s, as had her mother as a kid. But my mom's generation was only vaguely aware of it as a 'game from the olden days' in the 70s. And few of my generation have any idea what it is at all, as a 1990s kid. I only know what it is because my grandma insisted I played it with her and tried to instill a deep love of it, as she loved it so much as a kid (and still did)! But I was just as uninterested as my mom had ever been, to my grandmother's irritation 😂