How does Portia save Antonio from Shylock's clutches in the courtroom in Act 4 in The Merchant of Venice?
In act IV, Portia initially attempts to influence Shylock to show Antonio mercy by telling Shylock he should overlook the forfeiture. Bassanio even agrees to pay Shylock three times the sum of the borrowed money in order to save Antonio, but Shylock insists on having his bond, which is a pound of flesh. Portia then gives Shylock a knife to retrieve the pound of flesh but mentions that the law will not allow a drop of blood. She tells Shylock that if Antonio bleeds during the operation, the Venetian court is entitled to confiscate his land and property. After Shylock says that he would gladly take three times the payment, Portia tells him that he must enact justice. She also tells Shylock that if he cuts more or less than a pound, he will be sentenced to death. Portia then stops Shylock from leaving the court and says that there is a Venetian law that states,
"If it be proved against an alien That by direct or indirect attempts He seek the life of any citizen, The party 'gainst the which he doth contrive Shall seize one half his goods. The other half Comes to the privy coffer of the state, And the offender’s life lies in the mercy Of the Duke only 'gainst all other voice" (Shakespeare, 4.1.341-348).
Fortunately for Antonio, Portia was able to save his life and turn the tables on Shylock by the end of the trial. Her argument that Shylock must retrieve a pound of flesh without making Antonio bleed significantly impacted Shylock's decision to harm Antonio.
Well, I think "Shylock's clutches" makes him sound like some horrific ultra-ogre, which I'm not sure is the most sensitive reading of the text.
Shylock is pressing Antonio in the court to fulfil his bond, made legally, and which Antonio has agreed to: which states that if Antonio does not repay the loan from Shylock within the agreed time, Shylock can cut a pound of flesh from his body. Antonio does not repay the loan - and Shylock is therefore entitled to his bond.
And the court does not dispute this fact - until, of course, Portia realises that the bond does not say anything about blood. Shylock is allowed to cut a pound of Antonio's flesh, but if he removes a single drop of blood, he has taken more than he is entitled to - and the bond is forfeit. And that's how she manages to prevent Antonio from being cut to pieces: even if she does do it at the very last moment.