thats not a quad lol thats a 4 man clutch, It would be a quad if you killed them 4 players with a single bullet!
I got a triple headshot using the M40A5 with ACOG, If only I could record, it was amazing! I got my first quad yesturday, enemies were at bomb A in the terminal, I shot 3 of them with my pistol non of them died, I was low on ammo so I switched to my M40A5, and booom down the tunnel, QUAD!