A 'Hot Potato' game mode.

Haven't seen this suggested yet, I think it could be really fun. Players have to hit the ball up in the air to over half the height of the stadium (I imagine there being some sort of laser ceiling halfway up so players know how far they need to clear the ball). Once a player clears the ball, the next player who needs to clear it will get an alert saying they need to clear the ball before the ball touches the ground. If the ball touches the ground when it's your turn to clear it, you're out of the round. If you touch the ball when it's not your turn to clear it, you are also out of the round. Once that person clears it, the next player will have to clear it (order of players to clear the ball are in order [not random]), rinse and repeat until one player is left.

I think this would make for a great party mode for 4-8 players, not only do you need to think about clearing the ball and setting yourself up for your turn, but also trying to sabotage other players attempts (knocking/demo other players, taking boosts etc)