https://www.espn.com/mlb/story/_/id/...nnect-uniforms
Design inspiration: The Red Sox went with the most radical design among the uniforms released thus far, unveiling the first uniform in team history to feature yellow and blue as the primary colors. On the front of the yellow jersey, there is a blue stenciled font, and the hat is blue. While the team featured blue as a primary color through 1907, the team has primarily sported red since 1908. The Boston Marathon and Patriots' Day hold a special place in the culture of Boston, and the team decided to pay homage to the city's unique holiday through its uniforms, highlighted by the 617 marathon bib patch on the left sleeve.
These were designed locally. Sox are wearing them right now, because they wanted to wear them last weekend. Now that they are in a winning streak, they may be wearing them for a bit longer.