The statement that Samuel made to his father at that point was: “I have soccer practice today.” This implies that at the time when he was making this statement, he has yet to go for soccer practice scheduled later that day.

In this case, since we are recounting what Samuel said, the answer should be: “Samuel informed his father that he had soccer practice that day.“

Now imagine if Samuel had instead said this to his father: “I had soccer practice today”. This implies that at the time when he was making this statement, he had already attended the soccer practice for that day.

In this case, if we are to recount what Samuel said, the answer would be: “Samuel informed his father that he had had soccer practice that day.”

“He had practice that day” sounds correct

He had practice that day