Tanner Roark has a 1.78 BB/9 in one and half seasons for the Nationals. Currently, he has a Steamer projection of 2.26 for his 2015 BB/9. This value seemed a bit high to me. I went back and looked at the next season’s BB/9 for pitcher who threw at least 160 inning and had a BB/9 between 1.5 and 2.0.
Looking at all pitchers, the average BB/9 was 1.77 and jumped to 2.07 the next season. Since Roark is not as established, I limited the search to pitcher 27-years-old or younger and got a 1.77 BB/9 in season one and it jumped to 2.10 the next season. I looked at the median values to see if one high BB/9 was messing with the average, but the values were almost identical.
So if a pitcher does have an BB/9 between 1.5 and 2.0, historically they should expect a decent sized jump in their prediction for next season.