Perhaps Joy Boy's vice-captain?
Remember Usopp telling everyone he is the vice-captain, as well as Oda's early concept arts had Usopp as official vice-captain:
Then at some point, Luffy and Usopp fought;
Perhaps same thing happened to Joy Boy and his vice-captain, but instead of reuniting, they go different ways.
Of course, the difference would be that Joy Boy's vice-captain was probably a lot more stronger, close to Joy Boy's level, Joy Boy won in a tough fight, or that more powerful vice-captain betrayed him without any fight, and their crews separated into 2 groups.
Remember Usopp telling everyone he is the vice-captain, as well as Oda's early concept arts had Usopp as official vice-captain:
Then at some point, Luffy and Usopp fought;
Perhaps same thing happened to Joy Boy and his vice-captain, but instead of reuniting, they go different ways.
Of course, the difference would be that Joy Boy's vice-captain was probably a lot more stronger, close to Joy Boy's level, Joy Boy won in a tough fight, or that more powerful vice-captain betrayed him without any fight, and their crews separated into 2 groups.