Previously it was a grass field.  Per a 2010 article by Sarah Fenske in the Riverfront Times, Taylor Park was formerly the CWE Dog Park.  The city obtained development rights of the site as part of a recent deal that allowed Barnes Jewish Hospital to take over Hudlin Park, which was technically part of Forest Park, but located across Kingshighway Boulevard to the east.  You may remember the park that included tennis courts and playground equipment. (source)