Look at the person as they approach you. Is there anything you see that you can comment on or ask about?
If you’re at a sporting event, the topic of conversation is simple: talk about the team, the game, or the players.
How do you continue the conversation? Either with your answer to the same question or with the reason you asked it.
These are questions with no definite answer, they are subjective, and the answer is their personal preference or opinion.
It’s fine to bring up a topic the other person doesn’t know much about. But avoid topics that are too obscure or unlikely to interest many people.