First of all, CONGRATULATIONS to your son! I can think of little better than to attend a high academic college and be able to play the sport you love while there. What a terrific combination, and he's to be commended for putting himself in that position.
Suspecting that there was a better-than-average chance that my baseball-playing son might end up as a coach one day, I started early suggesting to him that he note carefully the words and behaviors of the various coaches he would have along the way. That way, he could build an ever-enlarging memory of those things to be imitated and those to be avoided once the time came for him to change the type of shoes he wore on the field.
Fortunately, he was the sort who would tend to accept his parents' advice (Even though, as a teenager, he might not always acknowledge it as being good advice!). In the process of observing, he learned some terrific traits; along with some others to shun.
As disappointing as your son's coach's lack of response might be, at least your son's learning a lesson that ought to lead him down a much more considerate path in the future when faced with similar circumstances.
All the best to him!