I was encouraged to see Dan take such a bold stance in even entering the A.J. Pierzynski Groundout Debacle of 2012 as a contender for Worst Play in the History of Baseball™. However, there really is no debate when it comes to this. It was actually another former San Francisco Giant, Ruben Rivera, who unequivocally holds this inauspicious title.
Don't just take Jon Miller's word for it. Judge for yourself. (Sorry for the grainy video, but this is basically the only version that exists. All other copies have apparently been burned for the well-being and betterment of all humanity.)