Jack, your last sentence might be true as you do not appear to be very well informed about the match process. For an 'S' position, an applicant applies during the fourth year, at the same time one is applying for the AOA internship. There is no conflict involved and it is the recommended route. Since the S positions are being increasingly sought after by DO students, you are providing incorrect and misleading information. As far as participating in both matches simultaneously being 'unprofessional', I suppose since none of us are paid to do it (in fact, it costs $80 to participate in the NRMP), it is an amateur act and not professional. Each year, ~5% of the fourth year DO students that match through the AOA do not sign the contract or ask to be released. The amount of legal action taken by programs...zero. If you are truly interested in 'unprofessional' behavior, and if you ever make it to the point where you are interviewing for an internship/residency, you will probably receive personal lessons from some of the AOA residency directors. Many are well versed in bending/breaking the guidelines for the AOA match. BTW, when do plan on starting DO school?