In The Merchant of Venice, how does the courtroom react to Shylock?
Your question would be a bit more clear if you had mentioned character names, if you are interested in reactions to Shylock and behavior. The courtroom itself cannot react to anything. For this answer, I will equate "courtroom" with the Duke, who is the arbiter of justice in the court of Venice. The scene is Act IV, scene i.
It is the clear from the opening words of his first lines that the Duke is biased against Shylock. He calls him:
A stony adversary, an inhuman wretch
Uncapable of pity, void and empty
From any dram of mercy.
These accusations, as far as the events of the play are concerned, are technically true, as least as far as the Christian characters are concerned. Shylock is the comic villain of this play, and as such, is painted as a bad guy, just as Don John in Much Ado or Malvolio in Twelfth Night are. Even though Shylock has a moving speech about the humanity of Jews, the character himself is very two-dimensional in his villainous designs, bent on revenge.
Once Portia turns Shylock's desire only for justice against him, instructing him that he must only take a pound of flesh for his bargain and no blood, she turns the tables on him once more, producing another law of Venice that states that if any "alien" (which Shylock is; being a Jew he cannot be a citizen of Venice) should make attempt on a citizen's life, he should forfeit all his lands:
And the offender's life lies in the mercy
Of the duke only. . .
And from this law, Shylock is stripped of all his lands and goods, but, owing to the mercy of the court (the Duke), his life is spared. The Duke says:
That thou shalt see the difference of our spirits
I pardon thee thy life before thou ask it. . .
And so, the courtroom of Venice begins the scene with a strong bias against Shylock, but ends the scene in good, Christian charity, granting mercy on Shylock and sparing his life.
For more on the trial scene and the Duke of Venice, please follow the links below.