Why did Rudy got himself disqualified from the final race of the day and then left his medals behind

Rudy spends the summer training for the upcoming Hitler Youth carnival, in which he intends to win four track competitions and show up Franz Deutscher, the Hitler Youth leader. Rudy wins the first three events but is disqualified from the fourth for two false starts. Later, Rudy tells Liesel that he disqualified himself on purpose and leaves his gold medals with her.

The image of Jewish prisoners en route to a concentration camp being "paraded" through Molching is a dark simulacrum of the Hitler Youth carnival, another Nazi civic event. The swift athletics of Rudy and the other runners contrasts with the shambling motions of the emaciated Jews. Both events are presided over by ambitious young followers of Hitler. Rudy appears to succeed in showing up Franz Deutscher, the cruel Hitler Youth leader, and he appears to do it on his own terms, willingly disqualifying himself from the final race. By contrast, the Jews are entirely at the will of the Nazi soldiers, some of whom only boys. Yet Rudy is also condemned, as the two agents who visit his home intend to recruit him for the military, in no small part because of his athletic accomplishments at the carnival.