What has made, or would make you justifiably forfeit a match, or pause to take a breather?
We've all done it at some point in BGs. If I've had dropped inputs that cause me to unfairly catch a combo and lose health, a "missed" hit that actually made contact with the defender, stubborn AI holding on to it's special, or waiting for the agonizing clock to tick down at the end of a fight, I just might go ahead and forfeit.