Many years ago when my son was playing travel baseball we were in a tournament that allowed the use of a DH and courtesy runners for pitcher and catcher. The opposing coach used the DH for the catcher. Later in the game the DH got a hit and the coach asked for a courtesy runner for his catcher. Ump allowed it and I missed it. Fortunately my score keeper had my back. I challenged the substitution, won, runner out. Since then I have always made sure I have an experienced score keeper, they make us coaches look so much smarter at times.