Absent highly unusual circumstances (e.g., an entertainment or sports contract), an employer can't enforce a notice provision - and even in those unusual contexts the remedy is to prevent the employee from taking a new job with another team or venue, not to force the employee to continue to work for the original employer against his will. Forcing somebody to work against their will would be a form of indentured servitude, and thus unlawful.

However, as jk suggests, there may be lawful penalties for resigning without complying with the extended notice requirement, such as reimbursement of certain expenses paid by the employer (training, relocation costs, signing bonuses), waiver of bonuses or commissions, and the like. What those provisions might be, and whether they would be enforceable? That's not something we can address without reading the contract.

Note, whether or not any consequence described in the contract is enforceable, nothing would stop the employer from telling future, prospective employers who call for a background check that you resigned without giving the agreed period of notice.