Inside MLB's potential new strike zone

Francisco Cervelli and Pirates pitchers are among those who benefit from the current strike zone. Justin K. Aller/Getty Images

ESPN’s Jayson Stark reported Monday that MLB has submitted a formal proposal to the players’ union to raise the strike zone -- particularly, the bottom of the strike zone, by an estimated 2 inches.

Let’s take a look at what’s behind the potential change, which players and teams could be most affected, and what it could mean for baseball going forward.

The growing strike zone

It’s no surprise MLB is looking to raise the bottom of the strike zone. The MLB strikeout record has been broken for nine consecutive seasons, and the growth in the zone –- particularly the bottom of the zone -- is a big reason why.

Previous research by Jon Roegele of The Hardball Times has shown that the bottom of the strike zone began to expand in 2011. The frequency of pitches in that area has remained consistent across the league since then, but the results have shifted dramatically (see the graph below).

In 2011, 24 percent of taken pitches in the bottom 2 inches of the strike zone were called strikes; that number has grown to 50 percent in each of the past two seasons.

As the strike zone has grown, hitters have been more aggressive at swinging the bat, resulting in more swinging strikes and fewer called strikes. But while there were over 3,200 fewer called strikes in 2016 than in 2011, there have been nearly 3,000 more called strikes in the bottom 2 inches of the strike zone.

Naturally, that has had a big effect on strikeouts. Consider:

• While called strikeouts overall have grown by 9 percent from 2011 to 2016, called strikeouts in the bottom 2 inches of the zone have grown by 194 percent over that span (171 in 2011, 503 in 2016).

• In 2011, the bottom 2 inches of the strike zone accounted for 2 percent of all called strikeouts in baseball; that number was 5.6 percent in 2016.

• Of the strikeouts at the bottom of the zone in 2011, 14 percent were looking; that number was 30 percent in 2016.

Who would be most affected by the change

Since strike zones vary from hitter to hitter – i.e., the bottom of the zone is different for Jose Altuve compared to Giancarlo Stanton -- it’s important to note that ESPN Stats & Information uses a dynamic strike zone, based on the top and bottom values PITCHf/x sets for each batter.

By parsing the bottom 2 inches of the strike zone -- the area that would be wiped out by moving the bottom of the zone to the top of the hitter’s knee -- we can see which teams and pitchers are most efficient at turning those pitches into strikes.

Over the past two seasons, no pitcher has recorded more called strikes in the bottom 2 inches of the zone than Jon Lester. Fellow Cubs starter Kyle Hendricks is second on the list. In fact, six of the top 10 pitchers on the list have pitched for the Cubs or Pirates over that span.

It’s no surprise, then, that the Pirates and Cubs have ranked first and second, respectively, in each of the past two seasons in called strike rate at the bottom 2 inches of the zone. Francisco Liriano leads the majors (minimum 300 IP) in that category (72 percent called strike rate) over the last two seasons, and Hendricks ranks second (71 percent). Both pitchers have benefited from their teams’ pitch-framing ability.

If we account for the strike probability of each pitch, which factors in how often a pitch is called a strike based on location and count, the Pirates (mostly with Francisco Cervelli at catcher) have been an MLB-best 16 percent above league average over the last two seasons at turning pitches down in the zone into strikes. The Cubs are not far behind at 12 percent above league average.

What would the new zone do for baseball?

One of Commissioner Rob Manfred’s priorities has been to improve pace of play. Consider:

• The average nine-inning game lasted 3 hours, 1 minute in 2016, the second-highest in MLB history (3:02 in 2014).

• There was an average of 3 minutes and 29 seconds between balls in play last season, up 19 seconds from 2010.

• 18.0 percent of pitches resulted in a ball in play last season, the lowest percentage on record (since 1988).

It’s unclear just how much of an effect raising the bottom of the strike zone would have on pace of play and the level of offense across the league. But by looking at offensive production in the bottom 2 inches of what’s been the current zone (the hollow beneath the kneecap), compared to what would become the bottom of a new zone (the top of the hitter’s knee), we can get an idea.

Over the last two seasons, batters have slugged .348 against pitches in the bottom 2 inches of the zone and .415 in the 2 inches just above that. Strikeouts have occurred 17 percent less often in the new zone while balls in play have happened 12 percent more frequently.