PROTOTYPE 2
43 Achievements
1,000
15-20h
Cannonball!
20 or more kills with a single Hammerfist dive attack.
10
How to unlock the Cannonball! achievement in PROTOTYPE 2 - Definitive Guide
Happy Hunting :)
It is most likely the easiest in the red zone, as there are always huge hordes of enemies running around, but you should be able to find enough people mostly everywhere after you get the range increase upgrade on the "weapon"
This can easily be done in the mission where you learn the Hammerfist ability. The mission is called 'A Nest of Vipers' and takes place on the second island (Green Zone). Once you get the ability from killing a juggernaut jump as high as possible and hold down the attack button to launch a Hammerfist Dive attack. There are lots of infected people in the lair which should make this easy.
You can also get this later in free roam or during other missions. It works best inside lairs because there are lots of infected close together. If you destroyed all lairs already then go to the center of the third island (Red Zone) and round up some infected on the streets.
In order to perform a dive attack while using the hammer fist, first jump into the air and hold the (Whichever it is assigned to) and you will crash into the ground dealing damage in a large circle around you. If you manage hit 20+ you will unlock this achievement. (See "You're the Bomb")