This requires a cooperative 2nd player.
How to: Choose Hardcore Mode and become a medic. Find a safe spot and kill and revive your friend with the defibrillator repeatedly. You get 80 points each time but you lose 15 for team killing.
Additional: Go to one of the areas where it will tell you that you are leaving the combat zone. Have someone walk out there and when they die run in and revive them with you defib paddles. You get 80 points and it doesn't take 15 points away for team killing.