Forbes attended Wesleyan and later Yale University. He played football at the tackle position for Yale University in 1905 and at the end position in 1906. The 1906 season was the first in which the forward pass was legalized, and Forbes caught one of the first big catches of the 1906 season. In her book, The Real All Americans, Sally Jenkins described Forbes' catch as one of the most significant in the first year of the passing game: "The only other significant pass that season was thrown by Yale, which gained a first down that led to victory over Harvard, when Paul Veeder threw thirty yards to Bob Forbes." Forbes was also a second-team All-American in 1905 and a consensus All-American in 1906, receiving first-team honors from Walter Camp for Collier's Weekly, Casper Whitney for Outing mag