If you think ED is a scam, don’t play. People who ED do so because they believe it conveys a benefit to them. It shows a lack of morals to me to not live up to your side of the bargain. Just because this involves a sport, there is no moral difference between this and a kid who gets in a “better” RD or EA school and tries to get out of the ED commitment, assuming there is not a legit financial reason.
Separately, and as a practical matter, if all we care about are selfish benefits, have you or your kid informed the coach of the second college that he has an ED acceptance in hand? Are that coach and that school wiling to be a party to this? If you have not and will not tell them, obviously you know this is wrong. What are the consequences if the second school finds out? Your kid could end up with no college if the second school rescinds admission because they feel you and your kid acted unethically. Finally, for your kid to be recruited this late, most likely he will be the at the bottom of the depth chart. Will he be good with that?
At some point you and your kid felt good enough about the first school that he was willing to ED to it. It’s not like going there is forcing him to go to Siberia.