Two Types of Green Monster Tickets
Above the Green Monster in left field at Fenway Park are the Green Monster seats. There are two different types of Green Monster tickets. The first type is a traditional Monster ticket. On most seating charts and tickets, these sections are listed as Monster 1 or M1, etc. These are reserved barstool seats with a ledge to put food and drink.
Standing Room Only Monster Seats
Photo Credit: Flickr, Peter Galvin
Just behind the traditional reserved Monster seats is a space reserved for Standing Room Only Monster ticketholders. This space includes a ledge for fans to lean up against and put concessions on - but there is no physical seat. Your best bet is to get there early and reserve yourself the best 'spot' you can.
For a more detailed description of the SRO option, check out this review on TripAdvisor from a fan who enjoyed his experience.