Dad of a Great Kid:
As usual Fenway's "two cents" are worth their weight in gold. I'm not sure I can add much, but at the risk of being redundant, here goes...
I'm sure that the Brown coach--whether the interim coach is made permanent or they bring in somebody new--will want to make his mark and distinguish himself from his predecessor. I bet that will translate into more rigorous training, practicing, and competition (both intra-squad and against other programs). No matter the Ivy school, the combination of playing on a team and the academics is a bear and the first year is usually a shock to the freshman system. Fitting four-hour practices and lifting sessions into an already tough academic environment is really really challenging. Time management skills are put to the test and getting assignments handed in on time while getting sufficient sleep takes focus and commitment. While there is a certain amount of institutional support, usually professors do not give athletes much extra leeway. Nor does the head coach.
If your son successfully walks on, he should be aware that the entire team does not travel to away games. So unless he is an immediate contributor and/or a stud, he may not travel with the team on weekends or to mid-week contests. There are benefits to this, to be sure, as it allows the players left back on campus newly found time to attend to their academics.
As Fenway remarked, it is essential that he introduce himself to the coach now and, once on campus, in person as soon as he can. He should make his intentions clear and ask the coach what he can do to improve his chances of sticking.
Good luck. Brown is a fantastic school and every year Ivy League baseball is getting better and better.