How do you know it will "ruin" a sport? It just might make it more interesting. Consider the extra strategy that will be needed and the intrigue as to how it will be managed. Which teams do manage it best and which teams have the deeper roster of high quality players will give the sport an added dimension of excitement. Imagine a division race where one team is down by 3 games but has all of it's key players for the last month and the other division members still have several key players yet to sit out. Imagine a team who normally wouldn't have a chance against a top team getting to play a team who is sitting out it's start QB. It gives them real hope of pulling off an upset. ... and I'm sure there are other intriguing scenarios to consider. But ..... No ... we can't change it because it's never been done before. Guess what ... everything that was done for the first time had never been done before.