Complex sentence: During the summer of 1880 he would cause still more controversy by moving to Blackburn Rovers, a local rival of Darwen, and stir up still more accusations of professionalism and claims that Blackburn has offered him improved terms.
Split into simpler sentences: During the summer of 1880 he would cause still more controversy by moving to Blackburn Rovers, a local rival of Darwen. The move stirred up still more accusations of professionalism amid claims that Blackburn had offered him improved terms.