This guide will show you a very easy spot to get this achievement early on in the game. During the second mission,
Operation Cobra, when you are assigned the objective "
Reach the AA Gun," you will see a barn with the roof blown out and Germans firing MG's on the second floor. Make your way to the barn, clear it, then wait on the second floor. All of your allies will group up here and start firing at the enemies below. Eventually, an enemy grenade will come flying into the loft area you're in and all you have to do is throw it back out. Because you have 5+ allies around you here, this should easily unlock the achievement (it might take a second to pop)!
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