Sansa attends a tournament held in honor of Joffrey's name day, a.k.a. his birthday. She took special care to dress nicely, hoping to avoid displeasing the king and receiving a beating from one of the Kingsguard.
While watching, she thinks back to the tournament held in her father's honor and how much more magnificent it had been.
During a match, Ser Dontos appears for the joust, drunk and missing his pants and horse. Pro tip: A horse is kind of a requirement for jousting.
Joffrey orders him to be drowned in a casket of wine, but Sansa pleads for the knight's life—with the Hound's help, she convinces the king that it is bad luck to kill a man on one's name day.
Sansa convinces Joffrey to make Ser Dontos a court fool while making him believe it's his idea.
Tyrion Lannister arrives with an entourage of his mountain men. He makes his condolences to Sansa for the loss of her father, and Sansa feeds him her practiced lie of how loyal she is to Joffrey.
Seeing through the lie, Tyrion promises to not hurt her.
Sansa remembers Cersei being kind before and reminds herself Tyrion is a Lannister.