As bones said, i think it's Lutheran H.S Athletic Fields. Or Gateway Park if you meant a further area near Jefferey.
"Gateway Park, a 71-acre public community park that is planned to include baseball and soccer fields, tennis and basketball courts, food concessions, parking and related facilities, is planed to be constructed in connection with the future development of the Orchard Hills community between Culver Drive and Jeffrey Road on the north side of Portola Parkway. .... Gateway Park will be owned and maintained by the City of Irvine. "