You are Required to not Hide Anything.
Assuming that both you and your date have an interest in the sport, going to a match together might appear to be an appropriate first date activity. But what happens if you don’t tell your date that the game is being played for the sake of your sister and that the rest of your family is going to be there? That will get you a red card, that much is certain.
It is acceptable if the two people have been seeing each other for some time, but going on a first date with a member of the same family on the field is not a good idea. Even if you were well-prepared for the action on the field, you still might not have the best day possible due to the awkward conversations you have to endure and the intense heat.