This is one of the fundamental rules of Top Eleven. All of your players drop 20% (lose 1 star) at the end of each season if you finish in the top 8 of the League and promote to the next level.

If you finish below 8th, you stay on the same level and your players maintain their star rating. There are exceptions to this however. I recommend that you have a good read through some old posts on here and you’ll see many topics explaining this.