So today I rolled a double in a battle with a friend of mine. Because of his character my damage got reduced to one out of three. So he said my knockback got reduced to one also? Is this true or does the knockback distance still stay the same?

I thought that since its base damage I should still make the knockback distance. But he said reduced means means less distance? Who's right here?

He's right. Knockback is equal to the damage dealt (which means if you hit someone with an object using Super Strength you can knock them back farther than your damage rating).

The exception is the Crusade TA, which knocks you back equal to the character's damage value every time doubles are rolled, even if you miss with the attack (except a critical miss).

Thanks for the info.