Rudiger was accused of "mocking" Takuma Asano by prancing while racing him to the ball. Rudiger was also seen laughing immediately after the incident.
However, Hamann says "there is only one team laughing now" after Japan caused a tournament upset by beating Germany 2-1 in their Group E game.
Speaking about the former Chelsea defender's actions, Hamann said: "Rudiger lifts up his legs and do you know. You don't belittle the opposition (like that) because it always comes back at some stage.
"I think it was very unprofessional. I think it was out of order. Arrogant. He was having a laugh, there's only one team having a laugh now.
"The spirit of the game is about respecting the opposition, respecting your opponent. And he didn't do it. I've got no explanation or excuse for it."
Former Arsenal midfielder Liam Brady also shared his opinion on the incident - saying Rudiger will feel embarrassed when he looks back on his actions.
Brady said: "He'll [Rudiger] be embarrassed when he sees that again and when he sees that result too.
"Because the Japanese got their own back on him. I think it was Asano he was taking the mickey out of. As Didi says, he won't be smiling now Rudiger."