Hriniak was a three-sport star at Natick High School where he was a first-team All-State selection in all three sports: as quarterback in football, center in hockey, and shortstop in baseball.

Initially a shortstop in the pros, Hriniak batted over .300 in each of his first two professional seasons, but in 1964, while playing for the Austin Senators in the Double-A Texas League, he was seriously injured in a car accident that took the life of a teammate (pitcher Jerry Hummitzsch)[2] and was on the disabled list for nearly three months.

[3] Hriniak would play only those few weeks in 1968 plus the 1969 season at the Major League level, for the Braves (by then based in Atlanta) and the San Diego Padres.

After Mauch's firing, Hriniak was reassigned to the minor leagues by Montreal in 1976, then was hired as bullpen coach by the Boston Red Sox for the 1977 season.

By the early 1980s, future Baseball Hall of Fame members Carl Yastrzemski and Wade Boggs, as well as All-Stars Dwight Evans and Rich Gedman, were Hriniak disciples.

He paid tribute to Charley Lau, who was the White Sox' incumbent hitting coach when he died from cancer at age 50 in 1984, by wearing his mentor's uniform #6 during his Chicago tenure.

Hriniak coached White Sox hitters for seven years, through 1995, before opening his own hitting school and becoming a private batting instructor.

When basketball great Michael Jordan surprised the sports world in 1994 by signing a minor league baseball contract with the White Sox, Hriniak was asked to help him with his batting technique.