Yankee Stadium has two distinct types of Standing Room Only tickets. The more sought-after of the two is Field Level Standing Room Only. These tickets are listed with a lower level section where you'll have an assigned standing spot at a drink rail.
The other type of SRO ticket is usually found in the Terrace Level where standing spaces are more of a free-for-all and views can be highly obstructed. Not surprisingly, these SRO tickets are often much less expensive than Field SRO seats.