Man, you guys in Iowa don’t really have a clue. You should come to PA where this is a science.
To the teacher with 753 years of experience- nobody that holds back their kid in 8th grade does so at the same school. Your K-2 example is with school buy in. With athletic holdbacks parents are solely driving the bus.
To the other dodos, nobody who holds back their kid in 8th grade pulls a gap year, there are laws about educating your children.
When kids are held back in 8th grade for athletic did purposes, they move from a public school to a private, parochial, charter, or home school situation and repeat the 8th grade. Then they enter 9th grade the next year. Sometimes staying at or going to a different private school, where you could say academically that was a pretty good idea anyway, or they head back to (usually a different) public or parochial school.
And this is pretty limited to a group of elite athletes (in all sports), thus saying it is common is in related to the small sample size, not the general population. This is a wrestling board, so that should have been fairly self evident, but as usual, wasn’t to some.