I look at the situation the other way. Not my son playing against holdbacks, but hypothetically if he were the holdback. One of my sons is really good. He is one of the top 3 or 4 players on his travel team and probably the best on his town PAL team. If I hold him back this Sept and have him play 5th grade lacrosse next season, instead of 6th grade lacrosse, it would be insane. I know for a fact he would be ridiculously dominating those younger kids. I can picture this conversation at the dinner table
Me” Johnny I’m going to have you repeat 5th grade this fall”

Wife and son” what are you talking about, Why would you want to do that?

Me” Because I want you to do even better in lacrosse”

Wife and son(as they stare at me like I lost my mind)” dad I’m doing great in lacrosse and school,What are you talking about?“

Me” yes Johnny you are, but I want you to be super duper in lacrosse. Playing against these younger kids, you will dominate.”

After my wife and son saw that I wasn’t joking, my son would probably go upstairs and cry. My wife would have me talk to some psychiatric professional. She would tell them my husband is losing his mind.