I have kids (and close friends with kids) that went thru the recruiting process at ND and other schools in Lacrosse, Soccer, and Swimming.
The scales are different by sport and school, but every school appears to have a minimum target SAT/GPA by individual, sport and for the school.
So (and using this example to get away from ND), Princeton has a swimmer target SAT but will allow a few swimmers in below the target SAT range as long as the average for all swimming recruits meets the team target.
More broadly, the swimming target might be a higher than the target in other sports so that the entire "student athlete" number meets a standard.
This will vary significantly by school. The target SAT/ACT is significantly lower at Maryland for example which makes sense as the requirements for all students is lower. A student/athlete at other schools can compete in the classroom without the higher GPA/SAT/ college prep high school background.
Each school manages this differently but the themes appear to be the same. Specifically at ND, getting a kid in at the minimums can be a problem. They need to be confident that the kid can maintain eligibility (and btw, the professors don't really care that the kid can run a 4.3 40.). The athletic department works to keep kids on track with tutors, study halls (required Freshman year) and very close management regarding grades - but this is not easy as we all know based on previous players becoming academically ineligible.
Not taking anything away from other schools, but it is hard to find kids that can manage both at ND.
So, they have to finds kids that want to work in the classroom that also have the ability. Not an easy task, and that holds (I think) for ND, Stanford, Vandy, Duke etc.