First off, it's intention and attempt, not the result. Like in other sports now, if you swing it's the same suspension as connecting a
punch but you can get sued if injured. I've seen many intentional headbutts, and it was 100% intentional (it was out of frustration) and if landed in
a bad spot at full impact that could cause a severe cut, broken facial bone, eye damage (vision; like Sugar Ray Leonard had a detached retina),
etc, etc...
Boxing is danferous enough, but headbutts are serious business along with rabbit punches. In 1995 a bout showed the accumulation effect of
on-going rabbit punches. Gerald McClellan had 31 fights with 29 by KO and 20 were in the 1st round with 2 losses and he was facing Nigel
Benn who had 39 wins with 32 by KO and 2 losses with a draw. McClellan was constantly receiving rabbit punches from Nigel Benn the entire
fight until the bout was stopped halfway into the 10th round when McClellan first took a knee for an 8 count, then he went down again and lost
consciousness. He went directly to the hospital after the fight. When McClellan was discharged to the care of his family, he was completely blind,
80% deaf and could no longer walk unassisted. A tribute thread I posted regarding him I added:
https://www.covers.com/postingforum/post01/showmessage.aspx?spt=39&sub=101104311 .
Now back to the question of the referee calling a DQ during a major boxing PPV fight. Remember Holyfield-Tyson II? With 40 seconds
remaining in round 3, Tyson bit Holyfields right ear taking out a one-inch piece of cartilage from the top of the ear. This was Tyson's retaliation
for Holyfield's intentional headbutts causing a large cut over Tyson's right eye at the end of the 2nd round. Mills Lane sae the damage, knew it
was a bite, wasn't sure what to do and head the ring doctor look over Holyfield's ear saying he could continue, but Mill's Lane took a 2 point
deduction that round from Tyson. During another clinch, Tyson bit Holyfield's left ear. Holyfield threw his hands around to get out of the clinch and
jumped back. Lane did not stop the fight this time, so the two men continued fighting until time expired. The men walked back to their respective
corners when the fight was then stopped. After 2 bites (1 on each ear and both were separate rounds and incidents) Mills Lane still let them
continue fighting until they got back to their corners. You often see headbutts, rabbit punches, cheap shots, holding and hitting, elbows and more.
Tyson biting an opponent on both ears it took out large chunks of cartilage was a whole new game. Boxing in the 1920's and 1930's was the first sport to make mouthguards mandatory. They were also called toothguards. They were basically preformed, thick semi circle of rubber that were worn over the top teeth. During a clinch and with the referee on your right side, fighters would lean left over the opponents right shoulder causing a blind spot to the referee. Fighters would then bite down on the back part of the neck right on the nerve (Trapezious Muscle and Levator Scapulae). So biting was nothing new, it just wasn't done much in more modern days with cameras and new mouthguards. Tyson spit his out along with chunks of Holyfield ear. The first fight there was a major accidental headbutt that opened a cut over Tyson's left eye and actually stunned him. If you watch the collision it was accidental and a severe blow that dazed Tyson, and leading to a 10th round stop as Holyfield pulled off the upset from being a 25-1 underdog originally when the lines opened. Apparently linesmakers forgot that 6 years earlier Buster Douglas was 42-1 underdog who KOd Tyson and giving him his first defeat. In the Tyson-Holyfield rematch, it was clear to me that Holyfield started to take advantage of the clashing heads styles and intentionally would headbutt Tyson. The first two rounds Tyson complained and Mills Lane did nothing because of the way Holyfield made it look accidental. After two rounds of headbutts and a cut, frustration turned to rage and the biting began and history was made!
Do you know the pressure and cajones it would take to stop a major PPV fight on a quick disqualification? The referee wouldn't get another fight and more than likely would be receiving death threats and on and on. People paid to see a fight, and $60 at home and over a grand easy for a seat inside the arena. Ali was known for not listening to the referee because he knew the implications back then. Even if a referee made a good stop but it looked prematurely to the fans, that man would be on the Most Wanted list. Ali's motto was "The referee doesn't pay me".
Roy Jones Jr struck Montell Griffin twice when he was on one knee. The punches weren't severe, nor did they appear to even hurt Griffin, but Griffin played dead and gave Roy Jones Jr his first defeat by disqualification.
These days with all the money involved I doubt you would see a quick early DQ unless it was at least a repetative foul in which the fighter was warned or penalized points, or if the foul causes a brutal ending in which the hurt opponent can't continue.