Possible Clues:

• Citi Field mascot
• Shea Stadium mascot
• N.L. mascot with a baseball head
• Big Apple sports mascot
• NY baseball mascot with a big head
• His head is a large baseball
• Big-headed major-league mascot
• Sports mascot who's a popular bobblehead figure
• Fifty-year-old mascot
• Rival mascot of the Phillie Phanatic