As far as I now you must have a mouse with extra buttons. Auto running is where you run and don't have to touch your keyboard or mouse.I accidently came across this "glitch" a while ago and just thought about sharing. You are able to do everything in game while this happens including turning, opening inventory, using steam overlay, anything. Now this doesn't seem to work with everybody as it has to do with your mouse and some mice work while others don't. If it doesn't work I'm sorry, I just thought I'd try putting it out there just in case it does work for others. This also works for vehicles you just have to assign vehicle keys instead of infantry (you can have both vehicle and infantry assigned to the same key). Bind move forward and turbo to the same key on your mouse. I have both assigned to my mouse button 4. To get to assignments configure>controls>assignments.While in game, hold down that button (you should start sprinting) and open up steam overlay keeping the mouse button held down. With steam overlay still up, let go of the mouse button and then you can close steam overlay.To stop auto running simply press the mouse button again or press escape.I hope this works for at least some of you, just thought I would try spreading the word.
