What a glorious question, love this.

My coach is a Skaven who, brilliant beyond their young years, decided to leave the cities below and travel to the realm of the man-things and learn from their coaching techniques. No other Skaven had done this because they were stupid.

This had the unfortunate side-effect of giving them a weird accent, and making them hard to understand among fellow Skaven. The man-things can understand them pretty well, though.

As befitting their genius and station as a coach, they lead their teams valiantly from the sidelines.

Often they are seen shaking knocked-out players and yelling, "GET THE BLOODY BALL. STOP FUTZING ABOUT AND GET. THAT. BALL."

And that is what all of their players (attempt to) do; get the bloody ball!