Possible to leave a contract academic position shortly after signing new contract?
The only real recourse that they would have is to sue you for breaking the contract.  Although that's possible, chances are that they wouldn't be able to prove substantial damages and that even if they prevailed you wouldn't have enough assets to make the suit worth while.  This is why academics who break their contracts are seldom sued for breach of contract.  

However, depending on how you do this you might end up losing any chance at a positive reference from your former employer.  This is probably the biggest risk that you face.