Complex sentence: In January he made his first appearance as a hot dog vendor at the Rose Bowl game Jack was attending where he became famous for the catch phrase "Pickle in the middle and the mustard on top!".
Split into simpler sentences: In January he made his first appearance as a hot dog vendor at the Rose Bowl game Jack was attending. As the hot dog vendor he became famous for the catch phrase "Pickle in the middle and the mustard on top!".