In photography, it is one kind of challenge to capture a single person in their environment in a engaging manner. Each person you add to the scene increases the difficulty. Each person must be engaging and in their own clearly defined space. You must be aware of the relationships between the people and their surroundings. Dancing with them as they move within the scene. If they notice you, you must decide whether to stay with the shot or walk away.
When they are engaged in something that is important to them (who will win the race), then you can just stand in front of them and wait for the moment without a worry.
Sometimes, it is just a matter of seeing the pattern of three blue caps flanked by white shirts.
From Santa Anita Racetrack