In Buford GA at the corner of Elm Tree Terrace and Buford Dam road, I was waiting for the light to turn on a decline. It is important to note that the car was driving in all-electric mode on a full charge. Once the light turned green I stepped on the accelerator to go and the car stalled. I believe the transmission slipped. The gears caught at high torque and jolted the car involuntarily forward. I didn't notice it at first but after a couple of sleepless nights with shoulder pain: I got an MRI and was found to have a torn rotator cuff. It is difficult to associate the injury as it is hard to access the force applied to the jolt. The only word I can use to describe the force of the jolt was violent. I believe there is a safety issue when a high torque electric motor is being run through a slipping or failing transmission and I suspect as a result I have suffered a injury as a result.