Cheers, yes some of it is in the game manual but a lot of people don't bother reading the game manual so I thought I would cover it here as well.
If you read the section on enthusiasm I explained it there, let me know if it isn't clear though.
I'll explain it here anyway just in case.
Playing at normal has NO EFFECT on enthusiasm. So if you didn't schedule a scrimmage the enthusiasm would drop exactly the same amount as if you did play the scrimmage. Every single day enthusiasm gets a little bit closer to 5, so when you see the enthusiasm change after the scrimmage, you might think it is because the scrimmage made the enthusiasm lower, but actually the scrimmage had no effect. the enthusiasm drops back down all by itself.