The baseball field shapes are called Terminal Area Arrival sectors (TAAs). If you are approaching the designated fix within the inbound courses specified (inbound between 085 clockwise through 265 degrees) and you are Cleared for the Approach by ATC without them specifying an altitude to maintain, then you may descend to 3600 MSL when within 30 NM of TOMHO and you may descend to 2800 MSL when within 15 NM of TOMHO. Of course if ATC specifies an altitude to maintain then you must maintain the assigned altitude.