In certain US states, it is illegal to fight any animal.
Check this webpage to find out your state's laws:
http://www.animallaw.info/articles/armpusanimalfighting.htm
For example (2 states on the east coast, 2 on the west coast):
NORTH CAROLINA:
(b) A person who owns, possesses, or trains an animal, other than a cock or a dog, with the intent that the animal be used in an exhibition featuring the fighting or baiting of that animal or any other animal is guilty of a Class 2 misdemeanor.
(c) A person who participates as a spectator at an exhibition featuring the fighting or baiting of an animal, other than a cock or a dog, is guilty of a Class 2 misdemeanor. (Punishable by imprisonment in a county jail for a period not to exceed one year, by a fine not to exceed ten thousand dollars ($10,000), or by both that imprisonment and fine.)
SOUTH CAROLINA
Any person who:
(a) owns an animal for the purpose of fighting or baiting;
(b) is a party to or causes any fighting or baiting of any animal;
(c) purchases, rents, leases, or otherwise acquires or obtains the use of any structure, facility, or location for the purpose of fighting or baiting any animal; or
(d) knowingly allows or permits or makes available any structure, facility, or location to be used for the purpose of fighting or baiting any animal is guilty of a felony and upon conviction must be punished by a fine of five thousand dollars or imprisoned for five years, or both.
CALIFORNIA
This statute forbids anyone from causing a fight between any animal of like kind (except dogs) or any animal (including dogs) from fighting with a different kind of animal or person for amusement or gain. It also forbids anyone from worrying or injuring any animal for amusement or gain, or causing any animal (except a dog) to worry or injure another animal. A person who allows such activity on any premises under his or her control, or any person who aids or abets the fighting or worrying of any animal is guilty of a misdemeanor.
OREGON
(1) A person commits the crime of involvement in animal fighting if the person:
(a) Owns or trains an animal with the intention that the animal engage in an exhibition of fighting;
(b) Promotes, conducts, participates in or is present as a spectator at an exhibition of fighting or preparations thereto;
(c) Keeps or uses, or in any way is connected with or interested in the management of, or receives money for the admission of any person to any place kept or used for the purpose of an exhibition of fighting; or
(d) Knowingly suffers or permits any place over which the person has possession or control to be occupied, kept or used for the purpose of an exhibition of fighting.
(2) For purposes of this section:
(a) “Animal” means any bird, reptile, amphibian, fish or nonhuman mammal, other than a dog or a fighting bird as defined in ORS 167.426.
(b) “Exhibition of fighting” means a public or private display of combat between two or more animals in which the fighting, killing, maiming or injuring of animals is a significant feature. “Exhibition of fighting” does not include demonstrations of the hunting or tracking skills of an animal or the lawful use of animals for hunting, tracking or self-protection.
(3) Involvement in animal fighting is a Class C felony.