To the OP, if you want to research this more, look at www.americangap.org
There are also gap year fairs across the country.
There are such great ways to spend that year. Some expensive and exotic, some just working, volunteering, job shadowing, and maybe taking some community college classes to get a few Gen Eds done. (Taking classes is not a bad idea! But verify how that might affect your future status as a true freshman vs as a transfer. ) There are programs that are very outdoorsy aka, outward bound or NOLS type programs that really foster independence and leadership.
It comes up fairly often in my neck of woods. But I don't claim to know much about the baseball implications, I guess he would have to find a way to play during his gap year to keep advancing (or at least maintaining) his baseball chops.
There are many ways to do a gap year but the primary advice I have is to be sure you have a place in a college freshman class, in case you change your mind, and/or to be sure you have a home for the following year! So, go ahead and apply to college as a senior. Get in to some of them (hopefully!) and go ahead and confirm a spot in a class at the one you like the most, THEN ask for a deferral. In that way you have a seat in a class so that you are completely starting fresh in your college plans as a 'gapper.'
(not sure that is a word!)
Why Harvard has been saying this for years is to try to get kids to chill a little bit I think. So while the number of kids who get IN to Harvard but DO take a year off are slim, the message is out there. If it is OK with Harvard then maybe my mom and dad will let me do it .... As I understand it, when Harvard admissions staffers speak at schools, they tend to bring this up, to help encourage kids at that high-pressure level to consider taking a break before they have a breakdown.
Will, it wouldn't have come up with a recruiting situation because they WANTED your boy that year!