Alright, I will prove why Teach was acting against Whitebeard, first of all, we must not forget that Teach is a good actor. He played the ”son” role for 20 years without anyone noticing that he was acting.
Blackbeard : ”I stayed on Whitebeard’s ship for decades because I knew that was my best chance of finding that Devil Fruit.”
- Chapter 440
Look how Teach was begging ;
Blackbeard : ”Stop! Pops! I am your son right?! You’re not really gonna kill me!” - Chapter 576
I think the message is obvious here. Teach tried to deceive him by using his weakness to his own sons, and he tried to deceive Whitebeard. But Whitebeard wasn’t naive enough.
Now we know that Teach was acting for years on Whitebeard’s ship as if he was his son. That’s for certain. So why not he couldn’t do the same thing when he could? I believe Teach was acting because Teach’s life was never in danger.
A : Because even after the Whitebeard’s final Quake attack, when Teach asked him to not do it, Teach was perfectly fine, he was cursing Whitebeard, and he could even draw his pistol and shoot Whitebeard it.
If he actually believed that WB could kill him with that Quake Attack he either doesn’t know his own durability level (Not only that then he was even fighting against the Fleet Admiral afterwards with no problem) or he was simply acting.
B : If Teach actually believed that Whitebeard could kill him, why not he called his crewmates before that begging part? He could kill Whitebeard before the begging part. Then why did he do that?
The only logical explanation is that Teach was trying to deceive Whitebeard ”once more” as he did for years. Luckily, Teach was acting and Whitebeard’s attack was ineffective.
*Theory by Erkan12