A "feature" of FB Mog is the forced "return to norm". If a player has a great season he will be permanently reduced in ability to ensure that he does not have two such seasons in a row. This, in fact, ensures that he never has two great seasons.

So, if at mid-season you have a player who is having a great year, bench him for several of your remaining games. Check you schedule for weak opponents and bench him in those games (or bench him in games you have little chance of winning).

I have contacted the developer to let him know that the "return to norm" should not be forced. It happens naturally. The likelihood of two consecutive 20% probability seasons is 4%. What the developer has done is not a "return to norm" but a permanent reduction to sub-norm.