Complex sentence: It also refers to the defensive unit of players that are positioned in the region: first baseman, second baseman, shortstop, third baseman and sometimes including the catcher and pitcher who as a tandem are often referred to separately as the battery.
Split into simpler sentences: It also refers to the defensive unit of players that are positioned in the region: first baseman, second baseman, shortstop, third baseman. Sometimes it includes the catcher and pitcher who (as a tandem) are often referred to separately as the battery.