The Strike Zone Is Smaller Than Last Year’s… For Now by Jon Roegele May 1, 2017 The strike zone. Depending on your opinion of baseball’s home-plate umpires, you may prefer to call it “a” strike zone rather than “the” strike zone. You may not know what to expect on any given day while watching your favorite team. Regardless of whether you think the calling of balls and strikes should be improved in some way, you at least have the option of knowing how the umpires’ collective zone appears objectively. For a decade now, every pitch thrown in the majors has been tracked. The position of every ball has been recorded as it crosses home plate. This extraordinary data has allowed for a quantitative assessment of what the strike zone looks like when aggregated over all pitches across the league. During this era, the called strike zone has expanded rather significantly, in particular at the bottom of the zone. This trend finally ended last season, when both the overall size and lowest section of the strike zone actually shrunk ever so slightly compared to the 2015 season. Now a month into the 2017 season, here’s a summary of the April strike zone relative to previous years. Strike-Zone Size for April, 2009-17 Year Overall Size Size Below 21″ April Season Diff April Season Diff 2009 432 435 3 2 0 -2 2010 432 436 4 7 6 -1 2011 439 448 9 7 11 4 2012 448 456 8 19 19 0 2013 453 459 6 24 30 6 2014 465 475 10 39 47 8 2015 465 478 13 46 50 4 2016 474 474 0 46 45 -1 2017 463 ? ? 43 ? ? SOURCE: Baseball Savant All numbers in square inches. So far this season, the strike zone — both overall and at its lower edge (around 21 inches above the ground) — most resembles those from April of the 2014 and -15 campaigns. The data suggest that the strike zone has tended to expand over the course of the season: full-season sizes are almost always larger than the April sizes. Of course, this may also just be a natural consequence of the strike zone gradually swelling and dropping lower over this period of years. Note that, in 2016, when the full-season strike-zone expansion finally ended, the April strike zone was very representative of the seasonal zone. The reduced zone size early this season compared to last is due to a tightening of the called strike zone for both left-handed and right-handed batters. Over the first many years of the pitch-tracking era, righties contended with a slightly larger strike zone than their lefty counterparts. As the bottom of the zone began to expand more rapidly in 2014, however, the imbalance between the lefties and righties also increased, leading to a double-digit square-inch difference between the two in each of the last three years. To date, 2017 has matched the 2016 gap. It’s hard to predict whether the strike zone as called in April will hold throughout the 2017 season, or whether umpires will allow the zone to inflate ever so slightly over the summer months (as has occurred in many of the tracked seasons). While baseball fans may have an interest in monitoring strike-zone developments, the commissioner will also be watching — to inform his decision of whether to push for a rulebook strike-zone change in the coming offseason. All we can do at this point is wait and see.