"Strike-zone judgment" and "plate discipline" are often used interchangeably, but there's a subtle-yet-important distinction between the two and it has to do with the whiff. Here's how I define the two similar batting traits.
- Plate discipline: patience at the plate, especially the patience to take strikes while waiting for your pitch.
- Strike-zone judgment: mastery of the strike zone to the point where you know whether any given pitch will result in a ball or a strike (simplification).
Essentially, strike-zone judgment is plate discipline without all of the free-swinginess. In statistical terms, a player with good plate discipline will walk a lot but may also strike out a lot. A player with good strike-zone judgment may walk a lot but will necessarily strike out only a little. Ted Williams had terrific strike-zone judgment, walking in 20.6% of his career plate appearances and drawing 2.85 walks for every time he struck out. Mark McGwire had terrific plate discipline -- he walked in 18.2% of his plate appearances -- but meh strike-zone judgment -- walking .83 times for each strikeout. So while Williams and McGwire coaxed walks with comparable frequency, the former struck out less than one-third as often as the latter.
In his only season with the Mets in 1962, Richie Ashburn walked 81 times and struck out just 39 (2.08 BB/K), which is the best Mets career mark for anyone with at least 400 plate appearances. In 2,965 plate appearances as a Met, Rusty Staub walked 333 times -- a nothing-special 11.2% walk rate -- but struck out just 204 times -- a terrific 1.63 BB/K.
If you thought Williams's 2.85 career BB/K mark was good, Eddie Collins walked 1,499 times to just 286 strikeouts, a walk-to-strikeout rate of 5.24. Tris Speaker was even better than Collins, posting a career BB/K of 6.27 (1,381 walks, 220 strikeouts).
The worst strike-zone judgment in 2009? That'd be future Met Bengie Molina, who walked just .19 times for each strikeout.