(Los Angeles, CA) -- Oklahoma head football coach Lincoln Riley is bolting for the West Coast. Riley will take over at USC, saying leaving OU was one of the most difficult decisions of his life. He replaces Clay Helton, who was fired in September after going just 42-and-24 in seven seasons in Los Angeles. Riley heads to USC after guiding the Sooners to four straight Big 12 titles and three CFP playoff appearances in his first four seasons in Norman.