Murray "The Mule" Marconi is a minor character who appeared in the episode "The Unnatural". A former sandlot player himself, he was teased by his fellow players for being the worst on the team. After physical training for his body and perfecting his baseball skills, he ended up being one of the most famous sandlot players of all time. Dog uses his success story to motivate Cat into working at his baseball skills.
Marconi shows up at the sandlot game, where he reveals that he is now an insurance salesman traveling around the world, and gives Cat a pep talk (who is still wearing the "Dog" mask), encouraging him that it's all about believing in yourself. However, Cat still strikes out and Marconi tells him that he really does stink.
He is also a judge in "Dog Show."