The question asks about the sport with which Sunil Chhetri is associated. Sunil Chhetri is a very famous Indian athlete.

Football Association of Sunil Chhetri

Sunil Chhetri is widely known for his significant contributions to the sport of football. He is a professional footballer who plays as a striker.

He has represented the Indian national football team for many years and is their all-time top goalscorer. He has also played for various clubs in India and briefly abroad.

Let's look at the given options:

• Football: As discussed, Sunil Chhetri is a renowned figure in the world of football, particularly in India.
• Basketball: Basketball is a different sport played with a ball and hoops. Sunil Chhetri is not associated with basketball.
• Boxing: Boxing is a combat sport. Sunil Chhetri is not a boxer.
• Billiards: Billiards is a cue sport. Sunil Chhetri is not known for playing billiards professionally.

Based on his well-known career and achievements, Sunil Chhetri is primarily associated with football.