As a high school AD, I get to deal with all types of complaints,etc from parents and students alike. Most of the time, once a parent calms down and you can have an adult conversation with them it works out. Keep in mind, this parent "probably" only has one side of the story which will be somewhat squewed by his child. None the less, assuming you have sound and logical team rules which you have presented to the team and their parents, vocally and on paper, and you have documented times in which team rules have been broken....you should be fine with your AD and Principal.
I guess as an AD, my question to would be; If there have been "persistent infringements" of team rules, how have you addressed these up to this point, and why was this not taken care of before dismissing the athlete from the team?
Best of luck. Let us know how the meeting goes.