Is this a sucker punch? A lightweight boxing match has revived an age-old debate.

• A boxing match last weekend reinvigorated the debate over what, exactly, is a sucker punch.
• The fight itself was a lightweight bout between Ruben Torres and Cristian Baez.

What is a sucker punch?

Typically, it's an unexpected punch.

In boxing, or indeed any combat sport, it specifically regards the type of punch that catches an opponent off-guard — perhaps when they're not prepared to defend themselves such as when combatants initiate a touching of the gloves as an act of fair play, but one swiftly delivers a punch, instead.

Floyd Mayweather knocked out Victor Ortiz this way in the fourth round of a Las Vegas fight in 2011.

Ortiz had attempted to head-butt Mayweather and continually tried to apologize to the boxer long after the referee said to box on.

Rather than accept a hug from Ortiz, Mayweather landed a one-two punch combination that finished Ortiz there and then.

This is when an allegation of a sucker punch, or cheap shot, becomes murky. If a referee has instructed participants to fight, the old adage "protect yourself at all times" comes into play.

Ortiz was not protecting himself after the referee instructed them to box.

Another such case happened Saturday, August 20.

A lightweight match between Ruben Torres and Cristian Baez reinvigorated the debate about what, exactly, constitutes a sucker punch.

In the video clip below, which the promoter Thompson Boxing posted on Twitter, Baez can be seen trying to instigate a touching of the gloves but Torres, instead, delivered a knockout blow.

Watch it right here:

The fight had previously been explosive with both boxers scoring knockdowns in the second round. In the seventh, Torres scored another knockdown because of a sharp straight right.

Baez protested the knockdown and claimed to the referee, Thomas Taylor, that it was instead a result of tangled feet, The Ring reported at the time.

The bout resumed as Taylor was satisfied Baez could continue, but Baez tried to touch gloves — something his opponent used to his advantage — as Torres then finished him with another big punch.

Taylor deemed the shot legal.

"They always say protect yourself at all times," said Torres, according to Boxing Scene.

"This is boxing, and fighters like myself are always on the attack. The referee gave the signal to start fighting again and I came out guns blazing, especially after I knocked him down.

"I hit him with a left hook and that was it, the fight was over. I'm ready to move on to bigger and better fights as I march up the rankings."

The bout took place at the Omega Products International Event Center in Corona, California.

Victory advanced his pro boxing record to 19 wins (16 knockouts). The 24-year-old remains undefeated.