Loss

From BR Bullpen

A pitcher is charged with a loss if he surrenders a run that gives the opposing team a lead that they never relinquish. Under the rules, a pitcher is considered to have surrendered a run if he allowed the runner who scored it to reach base, even if he scored while a subsequent reliever is pitching. This is analogous to the process for assigning earned runs.

There is always a pitcher charged with the loss in a game that does not end in a tie.