Sorry, I am kinda skewed toward working with numbers everyday. To help explain for a refresher (IF Needed)
If I remember things correctly, 2 (SD)standard deviations = 95% percent of all the samples are within a normal distribution bell curve. 3 (SD) standard deviations = almost 99.8% fit within the distribution. Maybe the number would be more like 2.5 SD (I think is 98% within the distribution). But the concept is the same, Identify the outlier in an objective, non-biased manner & decide how to deal with it.
Another way to think of this solution is to put all the school's coaches on the mid court line in the gym & ask everyone to take a step sideways for every transfer to the Right. To the Left if they actually lost transfers. Most schools would stop after only a few steps, with the most clustered in the middle. You would be able to see each year that most coaches only went so far. But the coach that keeps having to walk out into the right side of the gym will separate away from the group. OR IF every coach only takes 2 steps & 1 coach only takes a couple more steps, then no harm unless that same coach is always exceeding the norm. A pattern can be recognized and the Administrator can then work with that coach to correct the problem. Done & Done.
They should do that at all of the next conference, region, and state coaches meetings.