[1] This changed when A's outfielder Reggie Jackson showed up to spring training with a fully grown mustache which would later be thought of as the catalyst that sparked the move away from the conservative baseball era.
There had been some baseball players who grew mustaches, but all showed up cleanly-shaven (although long sideburns were acceptable) at the start of the regular season, either by their own decision or as ordered by their managers.
Initially, this assertion was not taken well by the organization and according to Mike Hegan, "(Owner) [Charlie] (Finley) told (manager) Dick (Williams) to tell Reggie to shave it off.
[6] To further promote his team's new look, every fan that showed up to the Oakland Coliseum that day wearing a mustache gained admittance for free; this numbered about 7,000 of the 26,210 in attendance, and all were treated to a 9–0 shutout win over Cleveland.
Meaning, the players would wear a green and gold pullover shirts on top, along with the traditional white pants and elastic belts.