Again, wrong. All running backs swing their arms. Try running without swinging your arms.
Murray's problem was that he didn't three point the ball. I said it over and over again. He carried it like a loaf of bread.
And running fast doesn't mean flailing your arms about. Best is to keep them at a 90 degree angle. Which is also perfect for cradling the ball and keeping it close to your body.
http://howdoirunfaster.com/speed-drills/tips-to-run-faster-using-proper-running-techniques/
4. Arm Position – When you bend your arms to run, be aware of the angle of your arms. The wider the angle of the bend in your arm, the bigger the arc of your arm swing. The smaller the angle of the bend in your arm, the smaller the arc of your arm swing.
You want to avoid a big and wide arc in your arm swing motion because it is unnecessary and a waste of motion.
I recommend that you bend your arm so that it is an acute angle (90 degrees or less) in order to prevent any wasted motions.
By maintaining an arm bend of 90 degrees or less you will be making significant improvements in all three areas.