Leo David Mazzone (born October 16, 1948) is a former pitcher in minor league baseball and pitching coach in Major League Baseball. He worked with the Atlanta Braves' organization from 1979 to 2005 and was the pitching coach for the Baltimore Orioles from 2006 to 2007.

Although Leo was born in West Virginia, his family lived on the other side of the Potomac River's north branch in Luke, Maryland. Growing up there, one of his friends was Sam Perlozzo of nearby Cumberland, Maryland, under whom he would eventually coach for the Baltimore Orioles. Mazzone was even the best man at Perlozzo's wedding.

After a moderately successful MiLB pitching career, Leo joined the Braves system and a mentor: Johnny Sain, who took the green pitching coach under his wing. (Sain, after an 11-year career as a major-league pitcher, had become a successful and well-traveled pitching coach.)

“Johnny was a little bit of a rebel,” Mazzone said, referring to the owner of 139 major-league wins for the Boston Braves, New York Yankees, and Kansas City Athletics. Sain was searching for a protégé to whom he could impart his baseball knowledge. Sain, who himself had four 20-win seasons, taught the finer points of his craft to nine men who also compiled 20-win seasons: Jim Kaat, Whitey Ford, Mudcat Grant, Denny McLain, Jim Bouton, Al Downing, Jim Perry, Wilbur Wood, and Stan Bahnsen. Leo willingly accepted Sain’s tutelage.

Both Mazzone and Sain understood that the art and science of pitching was changing. The days of the four-man starting rotation were relegated to the past. With five-man rotations, pitchers were throwing fewer innings and fewer times between starts. Leo was drawn to Sain’s revolutionary approach to the game. “He was ahead of his time,” Leo said, discussing his mentor’s unorthodox approach. “People were very critical. They feared his knowledge."

Since then, Leo has earned a reputation as one of the best pitching coaches of the modern era, having molded Tom Glavine and John Smoltz into perennial All-stars. Greg Maddux also enjoyed his best seasons under him. During his time in Atlanta, Mazzone developed and coached some of the best pitching rotations in baseball history.

In 2005, ESPN ranked the 1998 (#1) and the 1993 (#4) Atlanta Braves pitching staffs as two of the Top 10 rotations of all time. This dominant pitching anchored the Braves' run of 14 consecutive division titles (1991-2005), 5 National League pennants (1991-1992, 1995-1996, 1999) and the 1995 World Series championship. Between 1991 and 1998, three of his pitchers won a total of 6 Cy Young Awards, and Maddux, Glavine, and Smoltz have all been inducted into the National Baseball Hall of Fame. Over the years, a number of other pitchers joined the Braves and enjoyed some of their finest seasons under Mazzone only to regress after leaving.

Mazzone's "accidental trademark" is his rocking back and forth while sitting in the dugout. On television broadcasts of Braves games, the camera would often show him rocking back and forth during the game. Mazzone's pitching philosophies state that pitchers should throw more between starts (two sessions instead of one) and be able to throw strikes on the low and outside corner of the strike zone. That term velocity has ruined baseball,” Leo has said. “When I coached, it wasn’t about how hard you threw the ball but where you located the ball.”

In his book "The Baseball Economist", J.C. Bradbury titles a chapter, "How Good is Leo Mazzone?" Using statistical analysis, he analyzes whether Mazzone had a significant impact upon the pitchers that he coached. The sample is all pitchers who have pitched at least one year under Mazzone and one year under a different pitching coach. Bradbury found that Mazzone lowered the ERA of pitchers by an average of 0.64 points, and that after leaving Mazzone, pitchers' ERA increased by an average of 0.78 points. Bradbury believes that such an impact is deserving of Hall of Fame consideration. ESPN.com lists him number one on the list of "Top 10 Assistant Coaches of All-Time".

Since retiring, Mazzone has worked as a color commentator for Fox, and on August 30, 2016, Mazzone was named Special Advisor to the Furman University (Greenville, SC) Baseball Program. He was inducted in the Kinston Professional Baseball Hall of Fame in 1993.

(excerpted from SABR, BR Bullpen & Wikipedia)