Ryan you got it. In the past the 24 HR Le Mans race. The cars were on one side of the track, engines off. Hand brake on or in gear to keep them from rolling off. The drivers stood on the other side of the track. Flag drop to start the race drivers sprinted across to their car jumped in, .started the car and took.off. Now this was before seat belts and electronic communication between driver and pit crew.
Dr. Porsche had the driver have the key in.his left hand starting the car (was in neutral) while the feet and right hand released the hand brake and shifted the car into gear. Thereby gaining a few seconds on.their competitors. Usually meant getting out ahead of several cars.
So today the key/fob is on the left as Tradition!
And thanks all for the comments.