In Act II, Scene 4 of Shakespeare's Romeo and Juliet, what does Tybalt send to Romeo's house?
A letter. Tybalt sends a letter to Romeo's house. Benvolio tells audiences that detail early on in Act 2, Scene 4. The specific wording of the letter is not known, but the intent of the letter is known. The letter that Tybalt sends is challenging Romeo to fight a duel against Tybalt. Tybalt is still upset over the fact that Romeo crashed the Capulet party the night before. Lord Capulet told Tybalt to not worry about it, because he heard that Romeo was a good kid. He also doesn't want any fighting at his party.
Content thee, gentle coz, let him alone;
He bears him like a portly gentleman;
And, to say truth, Verona brags of him
To be a virtuous and well-govern'd youth:
I would not for the wealth of all the town
Here in my house do him disparagement:
Tybalt obeys, but he vows to get revenge one way or another.
I will withdraw: but this intrusion shall
Now seeming sweet convert to bitter gall.
Because of the letter, Benvolio and Mercutio are correctly worried about Romeo's safety. Tybalt is an excellent swordsman with a hot temper. He is not likely to forgive Romeo; therefore, Romeo is indeed in a lot of danger.
You can find the answer to this right at the very beginning of the scene.
Benvolio and Mercutio are together walking on a street. Benvolio tells Mercutio that Tybalt, who is a relative of Juliet, has sent a letter to Romeo's house. In the letter, he is challenging Romeo to fight a duel with him.
Mercutio and Benvolio are worried about this because Tybalt is a very good fencer. They are afraid he will kill Romeo.
When Romeo shows up in the scene, they stop talking about this and start teasing him about Rosaline. They still have no idea what is going on with him and Juliet.