Entering the ring marks the end of one battle and the beginning of another, one that can feel simpler to Heather Hardy than life’s day-to-day struggles. People often ask Ms. Hardy: Doesn’t it hurt to fight?

“It hurt to have my eight-pound daughter,” Ms. Hardy said with a laugh. “Nobody asks about that.”

She watched a client move around the ring at Gleason’s Gym in Brooklyn just a few weeks before defeating Anna Julaton at Bellator 194, a company that promotes mixed martial arts competitions.

For as long as Ms. Hardy, who is known as the Heat, has been a fighter, she has also been a single mother, raising her daughter with help from her sister, Kaitlyn. Without her assistance, Ms. Hardy might never have started practicing martial arts.