Challengers don’t let things stay the way they are, they go against something already in place, like a rule or the score on the scoreboard. Or they go after the same thing you may want, like victory in a competition or even the parking spot you were waiting for.
In earlier history, during the Middle Ages, a challenger was mostly a dreaded foe or someone who wanted to fight to the death with a sword. Some challengers want to challenge the truth or rightness of something, and that can be pretty serious too. In modern times, though, the word challenger often describes competitors who want to challenge each other in sports, on TV game shows, or in arguments. These challengers enjoy the challenge itself.