Do you have to Mormon to attend BYU and not be an athletes?

Answer 1

No. Although BYU is a university run by the Church Educational System (educational arm of The Church of Jesus Christ of Latter-day Saints aka Mormons) you do not have to be a church member to attend. The greater percentage of the students are LDS, however it is not required to be Mormon to play sports there. Important to note however, is that tuition is more expensive for non-members. This is because the church uses Tithing money of church members to subsidize the cost of tuition for other church members. The affordability of the church schools is a major reason they are so attractive, however prospective students should be aware that adherence to the strict "honor code" is required for eligibility on and off campus throughout a students entire enrollment period.

Answer 2

No. You do not have to be a member of the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) to attend BYU. In fact, you are more likely to be accepted if you are not Mormon.

Many students at BYU are not Mormon, they simply wanted to attend a good-quality university without the 'party' atmosphere that many other Universities have.