I have also received the purple heart once, I don't think it was a particularly bad day, if memory serves me correct I was a medic on the American team playing at Strike on Karkand. That's a frickin meat grinder until an American squad finally captures an enemy command post somewhere behind the "front line".
And by "particularly bad day" I mean it wasn't one of my worst, but my choice in job meant I wasn't going to get many kills anyways. Back when I first started playing I would get 1:10 ratios as a freaking assault, talk about your bad days.