Kangaroos actually can jump sideways—in fact, the only direction they cannot truly jump is backwards. However, their inability to jump backward is also somewhat of a myth. They can shuffle in reverse, just not actually jump. As far as sideways jumping is concerned, kangaroos can do so because of their tail.
Because kangaroos rely on their tails as much as their legs, they have the ability to hop around in just about any direction. With this said, the length and height of the hop will vary depending on which way he’s going.