I just checked AA.com but couldn't find "Yankees fan" in the chart of baggage allowance of "Sports Equipment" section,

the excerpt is as follows,

Antlers
Archery
Backpack/ Knapsack/
Bicycles
Boogie Boards
Bowling Balls
Camping Equipment

Golf Clubs
Fishing Rods
Hangliders
Hockey/ Lacrosse

Kayak, Boats, Sculls, Canoes ---Not accepted.
Pole Vault ---Not accepted.

Scuba Gear (with tanks)
Scuba Gear (without tanks)
Skis Water / Snow
Snowboard
Surfboards, Kiteboards, Wakeboards