Kristine Leahy will replace Jenn Brown as the NBC competition's sideline reporter. There's a change coming to American Ninja Warrior's seventh season. Kristine Leahy has been tapped to co-host the NBC's summer reality competition series, replacing Jenn Brown, The Hollywood Reporter has learned. Leahy will join fellow co-hosts and play-by-play duo Matt Iseman and Akbar Gbajabiamila this season.