No holds barred
Without restrictions or rules.
The holds here are wrestling holds and that's where the phrase originates. Wrestling has long been an Olympic sport, administrated by FILA, the sport's governing body. There are sets of rules for each of the
various styles of wrestling. Prior to the formation of rules, wrestling was a free-form affair. There was no need to mention any such phrase as no holds barred, as that was taken for granted. It wasn't until after the sport became regulated that bouts where those rules didn't apply were billed as such.
The earliest reference I can find to no holds barred is from Manitoba Daily Free Press, February 1892:
"Wm. Gibbs, the Kansas man, and Dennis Gallacher, of Buffalo, engaged in a wrestling match at the opera house here tonight. Gibbs was strangled into insensibility and may die. The conditions of the match were best two in three falls Greco-Roman style; no holds barred."
Forms of contemporary no holds barred wrestling in which rules are thrown out the window are Hardcore Wrestling and Cage Fighting.
Hulk Hogan starred in a 1989 film based on free-form wrestling - 'No Holds Barred'. Its tagline was "No Ring. No Ref. No Rules."