During the timeskip, Trafalgar Law was responsible for a major incident that came to be known as the Rocky Port Incident. While the exact details of the incident is currently unknown, Marine Captain Koby protected citizens during the incident and became known as a hero. Blackbeard managed to defeat Ochoku (Wang Zhi) with some form of assistance from Koby, making him the new boss of Hachinosu (Pirate Island).
Wang Zhi is the name of a real-life Chinese pirate in our world who is famous for trading Weapons with Europe, SEA, Chinese, and Japan.
So what happened? I can assume that the Rocky Port might not occur at the Pirate Island which is currently occupied by the Blackbeard Pirates. It most likely is occurring somewhere else. Law is causing a scene with an unknown purpose right now (possibly related to the 100 pirate hearts he gave to Marine or him trying to disrupt Doflamingo’s underground deal with Kaido).
Rocky Port might be a famous trading port which is used for normal trading by citizens and some pirates and also used for trade weapons. Wang Zhi might be either owner of the port and Pirate Island. Koby is there possibly for the SWORD to investigate the illegal weapon trading just like Drake reports to Koby that he sees CP0 trading weapons with Orochi.
So, what happens is that Law might lure Wang Zhi and his 100 trading pirate partners and attack him in the Rocky Port causing a scene in which Koby need to help evacuate the citizen around the port area. Law got all the 100 hearts of the famous pirates around that port. Koby might have a part in this battle (Law+Koby vs Wang Zhi and his gang). Deprived of manpower and his alliance to fight, Wang Zhi tries to escape and flees to the Pirate Island which was his base at that time. Blackbeard somehow knows that Wangzhi is in his venerable stage, so he does what he does best which is to attack people in their lowest strength. Blackbeard now takes control of the Pirate Island.
Something we still do not know is what Koby actually did in that incident, did he only save citizens or did he chase Wang Zhi to the Pirate Island? That is why Koby might have met Wang Zhi at the Pirate Island which ends up helping Blackbeard to take down Wang Zhi.
*Theory by Heydude1001