Tuesday, May 4, 2010
BIS: Baseball Info Solutions' fielding systems
By Ben Jedlovec, Baseball Info Solutions
Let’s take a look inside Baseball Info Solutions and the innovative Plus/Minus, Runs Saved, and Good Play/Misplay data that are being featured across ESPN this season.
Here’s an example from April 10 of this season. With one out in bottom of the ninth, two-time Fielding Bible Award winner Franklin Gutierrez chased an Elvis Andrus fly ball back into the deepest crevice of right-center field and made a leaping catch to rob a game-tying home run.
At the BIS office, our rigorously-trained video scouts were busy recording several detailed pieces of information into our scoring software. First, we recorded the ball’s location. Gutierrez caught the ball 383 feet from home plate, along Vector 161 (the angle 26 degrees off the right field line). Secondly, we track the ball’s flight trajectory and score it as either a bunt, ground ball, line drive, “fliner liner”, “fliner fly”, or fly ball. (A “fliner” is a ball between a line drive and a fly ball. A “fliner liner” is a fliner with a lower trajectory; a “fliner fly” is closer to being a fly ball.) The Andrus ball was a fliner fly. We also score each batted ball’s velocity as “hard”, “medium”, or “soft”. This particular play was a hard-hit fliner fly, as the ball was hit well enough that it almost left the park.
After recording each ball’s landing point and trajectory, we flag plays that fall into one of our “Good Fielding Play” or “Defensive Misplay” categories. The Good Plays/Misplays system, originally developed by Bill James, classifies 81 different categories of plays. For instance, a low throw scooped out of the dirt is flagged as a GFP 7 (“Handles Difficult Throw”). Back to Franklin Gutierrez - the Andrus hit was headed over the wall if he hadn’t made the catch, so we award a GFP 23 (“Robs Home Run”).
The Plus/Minus system looks at the ball’s location, velocity, and trajectory to determine the difficulty of the play. Of hard fliners (we group both fliner types together in the Plus/Minus system) to that location on the field in the past year, only 17% were caught. Confirming what our eyes told us, most fielders wouldn’t have made that play. We give him 1 - 0.17 = 0.83 plus/minus points, or “plays”. Additionally, all of the hard fliners hit to that location (at least those that stayed in the park) went for doubles when they weren’t caught, so we multiply his score by two (0.83 * 2 = 1.66). This is what we call “Enhanced Plus/Minus”, which we use to account for the play’s extra-base impact.
In The Fielding Bible – Volume II, we converted the Enhanced Plus/Minus scores to “Runs Saved”. For center fielders, every 1 Enhanced Plus/Minus point (or “base”, if you prefer to think of Plus/Minus in terms of “bases saved”) translates to 0.56 Runs Saved. Gutierrez’s catch results in 0.93 Runs Saved (1.66 * 0.56).
Of course, the play’s impact was arguably greater than that - he robbed a game-tying home run, after all - but that’s why we have the Good Plays/Misplays system to record more information about the play. By combining an entire season's worth of Runs Saved (which evaluates seven other aspects of defense as well) and Good Plays/Misplays, we get the most complete assessment of each player’s defensive abilities.