"Of the 128 quarterbacks surveyed -- 73 active, 55 retired -- 123 played at least two sports in high school (95 percent). About 60 percent played three or more. Five backups (Matt Flynn, Matt Barkley, Tom Savage, Aaron Murray and Zach Mettenberger) were the only respondents to report single-sport participation."
http://espn.go.com/nfl/story/_/page/qbsurvey150205HSTraining/high-school-specialization