Born in White Haven, Pennsylvania, he threw left-handed, batted right-handed, and was listed as 5 feet 11 inches (1.80 m) tall and 160 pounds (73 kg).

Mrozinski came up through the Phillies' organization, registering double figures in wins during each of his first four pro seasons.

Recalled from Triple-A Syracuse in the middle of 1954, he got into 15 games for the Phils, four as a starter, and split two decisions with a 4.50 earned run average in 48 innings pitched.

[1] Ten days later, Mrozinski earned his only big-league win, going 62⁄3 innings against the eventual world champion New York Giants.

This biographical article relating to an American baseball pitcher born in the 1930s is a stub.