I've had a few heart-pounding clutches in my time, but my most memorable one actually comes from a Native Battle match. The chips were down, I was a Nord Huscarl with Leather Armor, Round Shield, Nordic War Sword, and War Spear up against 7 other players. Even though this was more than a year ago now, I remember the team composition in fairly vivid detail.
They had two cavalry, three infantry (2 shielders, 1 Great Long Bardiche wielder), and two archers. I sought refuge in a small grove of trees to find some protection from the cavalry. The first cav charged me head on and was felled by one thrust of my spear. The details of what happened after are blurry, but I managed to kill the six other guys; of that much I am sure. The adrenaline rush I felt afterwards is probably the biggest high I've ever gotten from a video game, to the point where I had to stop playing for a bit.