CAUSING HAVOC by Lori Foster is the first book in her SBC Fighters series. She was one of the first, if not the first author to tackle the sport of mixed martial arts fighting in a romance series. Causing Havoc remains a favorite of mine. I just reread it this week.
Orphaned and torn from his sisters as a boy, sexy extreme wrestler Dean "Havoc" Conor gets a letter revealing how much his siblings want him back in Harmony, Kentucky. To stop his sister from marrying a sleazeball, Dean finds himself teaming up with her pretty-but-smart-mouthed friend Eve-who's heard of Havoc's reputation and doesn't need some hunk trampling on her heart. Now all Dean has to do is protect his sisters, win Eve over, and expose a devious criminal. And he thought winning the heavyweight belt was hard.