Medal of Honor: Frontline

There are many opportunities throughout the campaign to get this, you just need to cook a grenade and hope it hits 3 krauts. If you’re having trouble, then during Mission 6: A Chance Meeting, you will come across a scene where a Gestapo officer is inspecting the facility. In that same room, dispose of all enemies on the catwalk and any shooting at you below. Now move forward somewhat and turn towards where you came from. On the lower level you will spot an officer and two scientists, cook and throw a grenade at them and bam, trophy unlocked. Best done on Easy difficulty.

Level 14: Riding out the Storm is another good spot. There are 4 enemies sitting in the second train car and have nowhere to run when you chuck at grenade at them.