I could see this being a very eye opening game if you added "Fan" and "Parent" modes. In "fan" mode nothing you said would affect the game, although maybe a player would laugh once in a while. In "parent" mode, you'd have a youth soccer game where whatever you said would confuse the player and they'd perform worse.
Sounds like a fun project -- like a more interactive version of Football Manager.
Neat ideas.
One thing I am exploring is that, with LLM (and enough $ to pay the tokens) you can filter out offenses and hate speech in player communications.
All typed message is effectively translated by the LLM as “coach speech” and what is put in the UI is the LLM output. Sure, it is not exactly the player words and can get expensive, but I think it can be a good solution