Nebula was competitive in all things. Thor knew her well enough to know that much. It came from her background. Thor was similar, but less so, as even he and Loki had had pleasant moments as children, growing into the men they would become. They had a chance to be normal children, even as they trained and became warriors. Then their competitive sides had kicked in, as well as Loki's ambition to be the Allfather. In the end, though, Loki's hubris had gotten the better of both of them, once or twice.
Stepping up to the table, Thor took the controls for the red pieces on the board, grinning across at Nebula as she used the wrong terminology, but got close. "Touchdown is for a different game, I believe. This one, they just call goal. Let's play to... say, five goals to win? Sound good?"