Royloos' softball uniform is nice, but the jersey is different.  Softball jerseys have v-necks, as Royloos' product has, while most baseball uniforms have a placket that buttons down the front.  Perhaps something could be done with texturing.

The softball pants are short, with high socks.  That's the way baseball uniforms used to be, and some players still wear their socks high, but most wear long pants these days.

The batting helmet is also different.  (I took the above photo at a minor league game, so it has flaps on both sides.  Most major league players use a helmet that has a flap on only one side.)

The Corearts baseball uniform is pretty accurate and customizable.  It comes with lefty and righty batting helmets, and a morph that lets you change the pants from short to long.  It's easy to texture to match your favorite team, and I've used Wardrobe Wizard to fit it to everyone from Furrette to the Freak to Rosy Cheeks Lina. 

One thing I like about the uniforms Steve did for the Braves is that they're loose and drape naturally.  Dunno if it would be possible without using dynamic cloth.  These days, players wear their uniforms loose and baggy, and even the CoreArts uni has that skin-tight, Poser look.