If you're already 11 you should clearly be in 5th grade, if you choose to hold your kid back that's your decision and they benefit from that in sports. Just recognize that you're playing against younger kids, we could all hold our kids back a year and then they would be dominant too. Kids should play against kids there own age, that's what is fair, having an 11 year old play against 9 year olds and having that kid never come off the field is not cool or impressive.