When Robert had become King, Jaime was dismissed from the Kingsguard due to insistence by his father, Tywin. They had kept a Targaryen girl alive, and Tywin wished for Jaime to wed her. Which he did, no longer a serving member of a Kingsguard, Jaime had competed in Tourney's often.
Whilst Jaime prided himself in being a good fighter, he didn't take offense when was unhorsed and lost a Tourney. He took it with grace and honour. But what Jaime did not tolerate, was the Tourney winner declaring his wife as the Queen of Love and Beauty.
That was an offense, a slight upon her honour and a complete dishonour to Jaime. Which prompted Jaime to storm out to the Tourney grounds, unsheathing his sword before challenging the knight to a real battle.
"You fight well in Tourney's, but can you handle a real battle, boy?"
Jaime questioned with a raised brow as he pointed the tip of his sword at the knight who was now dismounting. Jaime could see his wife shaking her head no, as if she did not want Jaime to fight. But Jaime was determined to see it through.