+1 to kinnem.
I would add this:
This question has been asked many times on the SA forum. The typical answer is it can happen, but you need both branches in agreement, which is why it is a rarity. Plus, think of it like the NFL draft...if they are willing to let them go, why? It might be they have enough in that area, or it might be because they don't want them. The incoming has to decide which one of these options are the reason.
Additionally, they have spent money training them for 4 yrs, paying for summer training. What is the motivation to release them? What is the motivation to take someone if they have to re-train them their branch way?
Like knnems post here is my example:
AFROTC gives out rated assignments the spring of their junior yr. A/NROTC don't give out until their sr. yr.
Summer of their rising SR. yr AFROTC sends them to Wright Pat AFB for a 3 day flight physical. This is not cheap. Think of all the tests(incl. EKGs), flying them out there, per diem, etc. Why now when they are cleared should they hand them over to the Navy or the Army?
That medical file is available to any other branch, it belongs to the DoD...they might have to re-test something, but for AFROTC this is the FAA Flight physical. I would think only color deficiency would be an issue, and that would be for Navy. Yet the AF paid the cost and now they are losing a potential pilot that they had counted on for a manpower perspective.
The same with AROTC that sends cadets on summer tours for foreign language. Why would they agree to release them to another branch after paying for that?
Finally, if one branch is willing to release them, the question is if the gaining branch has the need for them?
I don't know which branch he wants to go, but for AFROTC as a jr., scholarship or not they will contract. They have control.
JMPO, unless he knows that no way in HADES he would go that branch, I would go ROTC. You don't know, he might fall in love with that branch.
If he is set on one branch, like our DS, than he needs to ask himself is the scholarship from age 18-22 as an athlete at that school is worth more than applying for the ROTC scholarship(branch) and being a walk on athlete at another school from 18-22?
Life is filled with compromises.
My kid, I would cover both bases. Apply for ROTC scholarship with intention of walk on, and pushing forward with the current situation.
OBTW since you haven't stated the branch, or the sport, place into the equation injury issues. Swimming, fencing, tennis, track that's one thing. Any injury will probably not be contact and cause issues later on. You can't say that for sports like FB, Basket Ball, LAX, Baseball, Hockey, etc., broken bones can trigger a DQ.
I am the odd duck. My opinion is strange. If you know you will never play that sport as a paid athlete, why put your body at risk? Many colleges have intramurals, and you can do it for enjoyment at a much lower risk of injury. Again, talking contact sports.
ROTC as a freshman is easy, 20 hrs a week is probably 2 times more than the avg cadet/mid. 20 hrs a week as a sr is probably not enough for the avg cadet/mid.
Like HS, demands increase as they rise up the ranks. Add in college courses, and a social life, sports and ROTC may mean their life is overload. That they are burning the candle not only at both ends, but in the middle too.
As parents, we don't want our kids saddled with college debt. We want them to go to college. We demand it. However, we are so self absorbed with the media talking about the debt of college students and the economy we lose sight that ROTC kids (AF/NROTC) will have a job for at least 4 yrs. 25K in student loans is not as bad as one might think. It is something they can handle.
Hence, why I am someone that shies away from taking a contact sport scholarship if their dream is to go AD military the day he graduates.
JMPO, throw it in the circular filing cabinet. It is your child and you know him the best. This is just me saying my opinion, and why.