It's common for kids to look up to the great players in a sport they play. They may even attempt to emulate the player's style to improve their game. At just 26, Brazil's Neymar Jr. is clearly one of the best active soccer players in the world. It makes sense that kids would want to ape his style.
However, the kids in the above video are mimicking Neymar only to poke fun at him after he became the World Cup's biggest meme last week. He earned the honor because he's spent a lot of time rolling around on the ground during this year's tournament. KFC even made a commercial about Neymar's rolling antics. So, these kids are practicing their best Neymar by hitting the ground and faking an injury.
He's notorious for flopping to the turf and rolling about in an attempt to draw a penalty kick or free shot. People have even gone so far as to add up the time he's spent on the ground during the tournament. (14 minutes!)