Even those of us who have followed baseball for years may not be intimately familiar with everything that goes on in baseball. For instance, we may have heard of a "simulated game"—particularly this week in the context of Josh Beckett's missed start due to concussion—but what does a simulated game actually entail?
Well, a little digging turned up a useful 2005 piece by Daniel Engber on Slate. From the piece, we can pretty much work out the basics, as well as the specifics. First off, simulated games are pretty much exclusively for the benefit of the pitchers (note the use of the plural). The goal, as the name implies, is to recreate as many possible scenarios that a pitcher would face in an actual game. The main difference between a simulated game and a real game is that a simulated game operates with a skeleton crew—beyond the pitchers, just a handful of batters (perhaps three per "team"—or just one set of three or four), one or two catchers, and the coaching staff.
No umpire is used—balls and strikes are called either by the catcher or the coaches, as are the results of any balls put into play, as no fielders are used. Similarly, no baserunners actually take up place at first, threatening to steal. However, if a base hit is "awarded," then the pitcher has to throw out of the stretch, and so forth. The hitters rotate until three outs are recorded. Then, to simulate getting up and down, a second pitcher takes his turn facing batters, and the process repeats until the pitchers have thrown enough innings or pitches.
Obviously, Beckett is not the only pitcher to have thrown simulated games recently. One story of note to follow out of the Nationals' training camp is the failure of Chien-Ming Wang to complete a scheduled two-inning simulated game. This is a major setback for Wang, who was hoping to catch onto the Nationals' roster in 2011 as a fifth starter. (It's also a setback for the Nationals, who have already paid Wang more than $3 million without his throwing a single pitch in an actual game.)