Metallica is at a loss for things to do since the retirement of Yankees relief pitcher Mariano Rivera. They are sitting around waiting for someone to hire them. Here's proof. At least that's what ESPN is implying with its new "SportsCenter" ad. The 30-second spot shows band members in the ESPN offices. James Hetfield and Lars Ulrich are trying to drum up a replacement for Rivera, who took the field to "Enter Sandman." The clip ends with Kirk Hammett in the ESPN breakroom offering guitar lessons. The Metallica "SportsCenter" ad begins running this week.