The player is not allowed to use its hands. Or, the player is not allowed to use her/his hands. Wich one is right? keep in mind, that gender of the subject is unknown. 聼起來自然嗎?

The grammatically correct way to say it is "the player is not allowed to use his or her hands" however, it is common for people to use "their" in this case because it's shorter. "Their" is only for third person plural but it is often used when the gender of the subject is unknown, even though it is not grammatically correct.

Also, only use "it" when referring to things that aren't people. "It" often sounds dehumanizing and derogatory when used to refer to people.