What is a "sacrifice fly"?

Which surgeon first performed Tommy John surgery in 1974? What is the "Mendoza Line" in baseball? What is the "infield fly rule" designed to prevent? What is a "balk"? What is a "pinch hitter"? What is the name of the spring training league held in Florida? What is the name of the spring training league held in Arizona? What is the highest level of minor league baseball?