The playing field at the new Arizona Bank One Ballpark (BOB) is the only field in Major League Baseball that faces directly north, unlike other fields, where the third-base line points north. The grass on the playing field is De Anza zoysia, a hybrid specially formulated for hot, desert climates. It tolerates low-light conditions well — an important factor when BOB’s mammoth retractable roof is closed during Arizona's hot afternoon games. The grass was developed by the University of California at Riverside.