Rocket Jump is an ability of Foot Soldier. It allows the Foot Soldier to jump to a higher place. It can be used to get to higher ground and have an advantage on enemies, as well as fleeing from burrowing Chompers. It takes 20 seconds to recharge. Its alternate ability is Rocket Leap and its plant counterpart is the Super Pea Jump.
Soldier Zombies take to the rooftops! The Rocket Jump ability enables the Soldier Zombies to get to places other characters can't. That's one off his bucket list for sure!
Do the same strategies as you would with Peashooter with Super Pea Jump, and use the Rocket Jump to get to an elevated position. It is very useful to take down plants from a distance. Remember to be stealthy while using it. On some maps, Rocket Jump can be really useful for getting to hard to reach places like the tops of houses. In last ditch scenarios, a good time to use this is to get out of a jam and to heal up. If a Chomper is burrowing underground nearby, this may be a good idea to use to get away. In Plants vs. Zombies: Garden Warfare 2, it may not be the best ability to use for this slot as Rocket Leap goes almost as high and you get two in that case.
There is really no direct way to counter this ability. You can only predict it. Simply try to, and if they use it improperly, it's one less way they can escape. Peashooters are likely the best counter due to their R1/RB/3 ability. It will allow you to chase the Foot Soldier down and vanquish them before they can run too far.