Claudius set up a fencing between Hamlet and Laertes and provide him with the chance of killing Hamlet, Laertes will use a sharpened sword instead of the normal fencing blade and he also added poison to his sword, this way, even a scratch of the sword will kill Hamlet. Besides that the king also set up a back up plan, so if Hamlet win the duel Claudius will have prepared a poison cup of win to celebrate.