It really was a wonder that no one had them figured out yet, neither of the two ever bothered to hide it and Yamaguchi was never good about being subtle with his infatuation in the first place. Tsukishima posited that the team had to be composed of a special kind of idiot for no one to notice their relationship. Yamaguchi suggested a kinder viewpoint, perhaps the two weren't as obvious as they thought they were, or maybe no one ever bothered to think about the nature of their relationship.
Either way, the couple wasn't averse to the team knowing about them, especially after Hinata had inadvertently come out as gay. Since the two knew they would be safe among the team, Tsukishima suggested a game to test their team's intelligence. And so, it began.
The rules were as such; they would progressively dial up the PDA in the company of the team, somewhere visible, but not too obvious. The affection would continue increasing until the team noticed or the two lovebirds decided to just tell them Here are the results.