Another easy trophy. This can be gain at any point but the easiest place is also close to the start of the game. After going through the intitial tutorial parts of the game when it allows you to free roam, Find a group of skag pups and shoot it enough to where its almost dead. Use the jump action and jump on top of it. Each jump inflicts a small amount of damage which is why you want it weakened first. Jump enough on it to put it down and this trophy is yours.
The skags do move around a lot while they're attacking you so you might want to kill all but one skag so you know which one you need to jump on.