Under the Ming tributary system, Japan could present tribute to the Chinese imperial court and be rewarded in the form of gifts by the emperor.
This was essentially an exchange of Japanese products for Chinese goods, and, being the only legal form of trade between China and Japan during the Ming's maritime prohibitions, was extremely profitable.
Despite this, Song Suqing was able to use his connections to bribe the head eunuch of the Office of Shipping Trade (市舶司), Lai En (賴恩), so the Hosokawa party was received first and got preferential treatment.
Enraged, the Ōuchi party went up in arms, killed Rankō Zuisa, burned the Hosokawa ship, and chased Song Suqing to the walls of Shaoxing.
For these reasons, the port of Ningbo was closed to foreign trade, but Lai En retained his post until 1527 and actually had his powers expanded to deal with military emergencies.
To protect their goods and recover their losses, the participants of the foreign trade armed themselves against the Ming military and engaged in piratical and smuggling activities.