Young 49ers receivers challenged by Kyle Shanahan’s complex system

Last year, as a rookie, 49ers tight end George Kittle had 43 receptions for 515 yards. Unofficially, he had a million mental mistakes. Just ask Kittle, who recently said his second-season improvement is tied to his better understanding of Kyle Shanahan's advanced-calculus playbook. "I know I'm a much better player than I was last year," Kittle said, "because my head's not cut off running around and not knowing what's going on." The message wide receivers Dante Pettis and Kendrick Bourne can take from this: Hang in there — it will get less confusing. In the first two weeks of the season, Pettis and Bourne, who have combined to play 15 NFL games, have run incorrect routes and both errors have placed them in an unwanted spotlight.