While I have not been cslled a hacker directly, I have caused many of my teammates to be accused of shooting through walls.
For example, I am a huge World of Tanks player. And I sometimes hop into my Artillery and drop down shells on others.
When an enemy gets damaged (sans crits), it doesnt say who the damage came from, so a lot of times an enemy will think he'd be hiding behind a rock, I'd drop a shell into his roof, do a measly sum of hurt that a tank on the other side of the rock could do, and my poor friendly guy gets confused as the victim of my rain of steel got hit and lashed out at him.