Not much has to be said about Ruben Rivera. He came to the Giants in 2003, after having worn out his welcome in previous stops. Mariano’s cousin started off well with the New York Yankees. But he stole some of Derek Jeter‘s gear, so he was let go. He then bounced around until ending up in San Francisco.
He appeared in 31 games that year hitting .180, and had one of the most memorable baserunning blunders in baseball history. You can view it here. It is still one of the greatest calls ever by Jon Miller.