[greymule]

"If on offense, the player is ejected, and declared out unless he has already scored." Just place the comma where it belongs.

True. You could insert that comma in hopes of preventing "mistaken junction," but don't count on readers to pick up on the subtlety. (Instructions that use this device invariably cause confusion among some readers. It's a no-no in methods and procedures.) Better would be "the player is ejected, and he is declared out unless he has already scored."

Your last example, of course, is fine: "the ejected player is declared out, unless he has already scored." Interesting that this one is correct with or without the comma, although the emphasis changes slightly.