Possible Clues:

• Letter in some fraternity names
• Greek letter; sounds like expression of outrage
• Letter before Beta in a society's name
• Greek letter that's also an M.L.B. city on scoreboards
• "Fie" homophone
• Letter that rhymes with the two that follow it
• The NFL's Eagles, on a scoreboard
• Feta was originally spelled with one
• N.L. East team
• Upsilon's successor