Shortstop throws warmup pitch

[lawump]

There is an official ruling from MLB Commissioner's office denying a protest which, by its nature, set a precedent for this issue. Billy Martin was involved in the game (shocking, huh?) back in the 1970's or 1980's. A protest was lodged (and subsequently filed) when the home plate umpire refused to acknowledge that the shortstop (or some other fielder) had become the pitcher (and thus required to face one batter) when he stopped on the mound on his way to his normal position and (fooling around) threw a warm-up toss to the catcher. The game was protested, and the protest was denied. Thus, the official MLB interpretation is that this action does not constitute a substitution. We learned this in umpire school.

If I am not mistaken this entire situtation was also laid out in some umpire's (auto)biography, too.