This trophy is misleading in a number of ways:
1. It doesn't have to be three unique players, meaning you can do this with two people total.
2. It can be done across one game, it doesn't have to be a single round.
3. It doesn't even have to be in a public game.
4. It appears that they have mixed up the descriptions for both this and Hotshot.
For each round, position your opponent on the bottom layer near the edge and spam snowballs at them until they fall off the edge. Repeat for two more rounds and this will pop.