Complex sentence: Around this time, allegedly a member of the Whiteboys (a secret agrarian organisation), he was wounded in a fight with soldiers and, fleeing to London to escape arrest, tried to make a living by writing.
Split into simpler sentences: Around this time he was wounded in a fight with soldiers, perhaps as a member of the Whiteboys covert agrarian organisation. Going to London to escape arrest, he tried to make a living by writing.