Answer: challenger

AnswerCrossword Clue
CHALLENGERBoxer who's vying for the title
CHALLENGERUnderdog, often
CHALLENGERProfessor in Doyle novels.
CHALLENGERChampion's adversary
CHALLENGERU.S. space shuttle
CHALLENGERFamed space shuttle
challengerone who challenges
challengerA US space shuttle that exploded 1.5 minutes after launch on January 28, 1986, killing its crew of seven