On Sunday, the trainee was Aaron Miles, a second baseman by trade who has also spent some time at shortstop. Miles has played a grand total of four games at third base in his big league career, but against the Mets, he got the call to start in place of Glaus.
"I know that there's not that guy that you think is the backup third baseman," Miles said. "I'm one of the infielders, so I'm going to have to focus in on making myself as comfortable as I can there. Hopefully it's a pretty easy transition. I'm not going to hope to make all the plays that a Scott Rolen would make, or Troy Glaus would make, but I'm going to try to play it to the ability that I know."
Miles hopes to make the routine plays, catch the groundballs and get the throws over to first. He also won't play quite as deep as Glaus, or his predecessor, Rolen.
"As a rule, third basemen play too deep anyway," manager Tony La Russa said. "So you get in to where you can make plays having some forward momentum, and that makes it a more comfortable throw rather than having to back up -- just react to the ball off the bat."
Miles had no chances at third base on Sunday, though a couple of balls were just out of his reach.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.