Redshirting is very common in our area. 2 of the kids in my neighborhood with early June birthdays were held back a year before starting K, and the school district recommends holding back children with summer birthdays even though the cut-off is Sept 10. In our district, the redshirting is not being done for sports, but for academics. They make a huge deal out of making sure the kids are "ready" for kindergarten by requiring kindergarten readiness testing, and if a child is born during the summer they almost always recommend waiting a year regardless of the results.
It does set up a strange situation in the school, with each class having a wide range of ages. For example, in my sons' first grade classes, there will likely be kids who were born between June 2006 and early September 2007, which is a sixteen month age spread.
Sports other than the official middle school/high school teams are done by age, not grade, so redshirting isn't possible.
