Wrestling legend Kevin Nash is officially off the hook in the Christmas Eve brawl with his son -- after cops determined "Big Sexy" wasn't the one who started the fight.
We broke the story ... both 55-year-old Kevin and his 18-year-old son Tristen were arrested at the family home in Florida after an allegedly drunken Tristen got physical with Kev.
According to the police report, Kevin took Tristen down to the ground hard after Tristen spit in his face. Tristen claimed Kev used his signature choke-slam move and caused him to black out.
But now officials tells TMZ Sports the State Attorney's office investigated the incident and determined "Mr. Kevin Nash was not the primary aggressor in this situation and that criminal charges should not be filed against him."
As for Tristen ... officials say he's not in the clear -- they're still investigating his role in the fight.
We spoke with Kevin's attorney Michael Politis who tells us, "Kevin is very relieved this got done quickly because of his career with the WWE and his potential induction into the Hall of Fame."
"He didn't want to be placed in the same category as -- for example -- the NFL player who punched his wife in the elevator."