Complex sentence: Riley and Mark Radcliffe formed the parody group The Shirehorses who played at Glastonbury in 1997 in what they called the headline slot going on as they did at 10am they did shows in various parts of the country including one supporting Blur.
Split into simpler sentences: Riley and Mark Radcliffe formed the parody group The Shirehorses who played at Glastonbury in 1997 in what they called the headline slot, going on as they did at 10am. They also did shows in various parts of the country including one supporting Blur.