What do you think....?

I have been in my job for 9 months. I was recently assigned to a certain position and was switched, I asked my supervisor why this happened. He stated to me that he was not sure if I was "capable" of the postion and that he did not "want to set me up for failure". I convinced him that I should have a chance to do my job and he let me in that position. When I came back from my days off, there was a person that never work that position (and was male and I am ) and I asked if anything was said to him about being capable of doing is job. he said no. Does this sound like it is possible discrimination.

NO, you were given a reasonable and thoughtful answer, it appears they are looking out for your well being. Discrimination only applies to sex,religion , race. none of these were involved.

No. Your boss identified no protected categories when he made a business decision to move you from the position.

If he had made any comments related to your gender, sex or that a male would be better in the position, then it could be considered discrimination.

While the individual who was placed in the job may have said he was not questioned about his abilities to do the job, it is of no consequence because the employer can choose who they wish to fill a position, regardless.

Hope this helps.