Game mechanics here states that illegal position of player is every time he is in position that he does not have written in his skills. Exclamation mark states that he is not in his trained position.

DC CANNOT BE ST. Of course DC CAN SCORE GOAL. Put GK as penalty shooter and eventually he will score goal from there.

This worked for me. I was angry when players got injured for long period...so I stopped being angry and got new players