I'd say these have to be the stirrups (stirrup stockings/socks), the ones that go on top of the sanitary socks:

In baseball’s early days, the dyes used in stockings were not colorfast, so a spike wound could easily get an unhealthy dose of colored dye. Wearing a white stocking underneath the colored hose would help eliminate the problem, but the double thickness of socks meant that a player’s shoe no longer fit properly. The solution, introduced during the first decade of the 20th century, was the colored stirrup stocking. The innovative sock allowed for a protective layer of material around the leg but a single thickness of material in the shoe. Since the white stockings worn underneath the stirrup stockings provided a sanitary layer of protection, they were dubbed “sanitaries.”
http://en.wikipedia.org/wiki/Baseball_clothing_and_equipment

Here's what they look like:

http://www.baseballjunk.com/stirrups.htm