"The on-field look of MLB received a much-needed jolt of energy in 1963 when Kansas City Athletics owner Charles O. Finley garbed his team in “Kelly Green and Tulane Gold” uniforms. A man ahead of his time, Finley paved the path toward the modernization of the design of the Major League Baseball uniform that reached a crescendo more than half a decade later.
On the night of July 16, 1970, the Pittsburgh Pirates christened Three Rivers Stadium with a 3-2 loss to the Cincinnati Reds. In a surprise move, the Bucs unleashed a new set of uniforms for the occasion – pullover jerseys and beltless pants made of a synthetic stretch material, 60 percent nylon and 40 percent cotton. The new outfits were radical in their appearance.
“There are no buttons on the shirts or pants, which resemble ski pants,” reported the Pittsburgh Post-Gazette."