Although he occasionally played softball as a teenager, his relationship with baseball began by an unusual approach—after he enlisted in the United States Navy in 1942, Zapp joined a segregated military team while stationed in Pearl Harbor, Hawaii.

[1] Impressed with his performance on the field, coach Edgar "Special Delivery" Jones—a former running-back in the NFL—transferred Zapp to his white team, making him and first baseman Andy Ashford the only two black players to join the integrated line-up.

[citation needed] While stationed at Staten Island, New York, Zapp was signed by the Baltimore Elite Giants as a backup corner outfielder, initially on a weekend basis, then full-time for the winter season.

[3] The following year, Zapp played for the Atlanta Black Crackers, showing a hint of his power hitting by knocking 11 home runs in half a season.

[5] When Norm Robinson, the center-outfielder before Mays, returned to the Black Barons after recovering from a leg injury, he was inserted into left field to utilize his defensive prowess, briefly displacing Zapp from the everyday line-up.

[6] Despite his diminished role, he played a crucial part in leading the team to winning Negro American League pennant in seven games against the Kansas City Monarchs.

[3] A recommendation by fellow former Negro leaguer Butch McCord in 1952 persuaded club owner Josh Gibbons to sign Zapp to the Paris Lakers of the Mississippi-Ohio Valley League.

[3] For his second season with the Broncs, Zapp struggled defensively after being shifted to first base and was traded to the Port Arthur Sea Hawks, adding eight home runs and 37 RBIs during his stint.