Eastbay Sleeveless Poly Jersey - Boys' Grade School Suit up in the Eastbay Sleeveless Poly Baseball Jersey. This 100% polyester knit baseball jersey features moisture management technology which wicks sweat away from your body, leaving you cool and dry during the pressure moments of the game. This jersey is great for customization and gives your team the winning look. Join the team with the Eastbay Sleeveless Poly Baseball Jersey. Imported.