This trophy is titled "
Range Attacker" and it requires you to get 10 Grenade kills in a single online game.
From the Main Menu of Rogue Trooper, select ONLINE and choose CREATE PUBLIC GAME. Once the lobby has been created, select the
Button to start the match by yourself. The map should already be preset to EPICENTRE.
Once the game loads, proceed forward and several enemies will attack from a cave ahead of Rogue, and to his right. Simply toss your frag grenades at them, killing however many you can per grenade. More enemies will swarm out of the cave as long as you hold back. Once you're out of frag grenades, press left on the d-pad to switch to sticky or incendiary grenades to wrap up your 10 kills, unlocking the trophy.