Jaap was born in Bellshill, Scotland, and moved to the United States with his family when he was a child.
His family settled in Pittsburgh where he grew up playing soccer from a young age.
He began his career in 1912 with a series of amateur and semi-professional teams in the Pittsburgh area.
In 1921, he moved to Philadelphia Field Club of the first division American Soccer League.
In the Challenge Cup, a 7–2 win over St. Louis Scullin Steel F.C., Jaap scored one of the Bethlehem goals.