There has been a sense that Duffy's command is settling into an above-average range after an adjustment period upon entering the Majors, so I decided to graph the progress of Duffy's walk rates over his 11 MLB starts.
Walk rates stabilize fairly quickly as baseball statistics go such that a sample size of only 30 innings can give you a pretty good sense of a pitcher's command. Plotting each start on its own will show mostly random noise, so I chose to plot a moving average with each data point reflecting Duffy's previous 4 starts up to that point. (The first data point shows Duffy's BB/9 over his first 4 starts, the second data point shows starts 2 through 5, etc) This gives an average sample size of just over 21 innings per data point which isn't a rock-solid indicator of future performance, but should be enough to show real changes in performance over time.