It's about honor, respect, and sportsmanship. When Mr. Xu realized the superiority of his martial art form, he should have behaved himself in a more dignified manner: let his superiority show without giving his opponent a beating.

It's still a fight. giving an inch, or letting up allows your opponent back into the fight.

What you are alluding to is the idea that he could beat him with a hand behind his back so to speak. (Which might be true) but could be perceived as even more disrespectful imo.

Not sure if you're being sarcastic. How exactly would he do that?

By not continuing to pummel him when he is on the ground. I don't know what could compel someone to continue hitting a person's head as he lays helpless on the ground (the opponent was basically curled up in the fetal position). At that point it just seems like the fighter gets some sort of sick enjoyment from hurting the other person.

The referee is supposed to stop the fight when one of the fighters becomes unable to defend himself.

Sure I get that. But how far do you take that justification? Would you be willing to kill someone who is laying on the ground defenseless because the referee is inept. Fighters need to have some self control. And it in this specific situation it seemed pretty cut and dry that the Tai Chi master was not able to fight back.

Haven't you ever seen a Kung Fu flick? This is an entire trope.

That's not the author's words. That's just the words of some random passerby of the studio that the author quotes. I would assume Wei Lei, in taking the challenge, felt otherwise.

I think it probably didn't help when Wei Lei brought Mr. Xu's mother into it.

Joking aside, I don't know what's to be gained by smashing a clearly weaker opponent unless you are a sadist.