Complex sentence: As Franchitti crossed the start/finish line to finish the race, the Scotsman who had not realised the chequered flag had been waved continued to race and crashed into the back of Kosuke Matsuura flipping yet again and hitting the outside wall.
Split into simpler sentences: As Franchitti crossed the start/finish line to finish the race, he did not realise that the chequered flag had been waved and continued to race. He crashed into the back of Kosuke Matsuura flipping yet again and hitting the outside wall.