Possible Clues:

• Opposing team
• Strong competitor going against you
• Ares, to Wonder Woman
• Situation depicted at 39-Across
• Enemy in sports
• Hamilton, to Burr
• Focus of one's enmity
• Athleisure, e.g
• A Stark, to a Lannister, on 'Game of Thrones'
• Enemy following old European