How do you knock down cars in Asphalt 8 multiplayer?
In multiplayer, knocking down people is harder than in single player to make it more fair for everyone. You must either (a) ram them at a high rate of speed, but not too fast (you don't want to wreck instead), or (b) grind them against the wall.
The main rule is that you must have a higher speed than the other guy at the moment you hit him. So always use your level 3 nitro boost when knocking down someone.