It's a niche that relies heavily on the author knowing the sport well enough to not make silly errors, but not so well that they bore the reader with minutiae. The sweet spot is using the sport as a metaphor and a source of natural conflict. A play that fails becomes a metaphor for miscommunication. A winning strategy becomes a metaphor for how they work as a couple.
Readers who love sports will appreciate the authenticity in the background. Readers who are there purely for the romance will follow the emotional beats. The best books in the genre manage to serve both masters, using the specifics of football—the aggression, the strategy, the teamwork—to deepen the character and relationship development in ways another setting couldn't.