The ABS Challenge System had indirect impacts beyond the challenges.

As you know, this season the ABS challenge system arrived in the Majors. What you may or may not know is that the initial ball-strike calls had a higher accuracy this season.

Let’s focus more specifically, on the overall accuracy of umpires calling pitches just outside the strike zone.

This season, when a batter does not swing at pitches just barely outside the strike zone, it is almost three times as likely for the umpire to call it a ball.

“…Balls just off those three edges [excluded top of zone] were called strikes 37% of the time in 2025; they’re being called strikes 13.5% of the time in 2026….” Ben Clemmens, 12 May 2026

This season through 8 May, walks as a percentage of PAs increased 1.11% (from last season’s 8.41% to 9.62%). This season’s rate is the highest shown in Baseball Savant (which included the 2008 season onward).

Recently, walk rates for Diamondbacks batters changed.

In the four previous seasons, the Diamondback batters had higher walk rates than the league averages.

This season in games through 8 May, something different happened. The Diamondbacks batters had a lower walk rate than the league average (7.53% vs 9.52). Perhaps batters were being too aggressive and not taking walks.

Then, in the recent five games (9-13 May), the Diamondbacks batters dramatically turned it around. In contrast to the league average (that dropped from 9.52% to 9.08%) the Diamondbacks increased their walk rate from 7.63% to 11.89%. Very impressive!

The following table compares the walk rates of the Diamondbacks batters and the league average. Data from Baseball Savant.

Did the increased walk rate directly result in more runs? Yes. The extra four walks resulted in two extra runs. Extrapolating those five games to an entire season would be an extra 64.6 runs! The following table shows the impact. Data from Baseball Reference.

One situation that can greatly impact the game is the 3-2 count. Whether the pitch is in the strike zone is the primary driver on the batters’ swing decision. A secondary driver is whether pitches just barely outside the strike zone will be called balls (which you may remember is three times more likely than last season).

The following table shows Diamondbacks batters in 3-2 counts. Excluding foul balls, 16.7% of their swings were successful (they got a hit). More remarkable was that when they did not swing their success rate (they got a walk) was much higher (88.9% to 100%).

The walk rates for Diamondbacks pitchers changed.

In the last four seasons, the Diamondbacks pitchers made a steady improvement in their walk rates compared to league averages.

This season through 8 May, their walk rate increased by about 10% over last season, which was barely better than the league average.

In the last five games, their walk rate dropped dramatically (from 8.87% to 6.43%). I’m not sure such a large improvement is sustainable.

The following table compares the walk rates of the Diamondbacks pitchers and the league average. Data from Baseball Savant.

The Diamondbacks Rockies Series at Coors Field.

What about walks at Coors Field? Will the ease of hitting at Coors field (and pitchers’ attempts to avoid the strike zone) make the changes in walk rate more pronounced, or less pronounced?

In the first two games of the Coors series, Diamondbacks batters walked 12.0% of their PAs. Which was the same rate as 9-13 May.

In the first two games of the Coors series, Diamondbacks pitchers walked only one batter, which was an astonishing 1.5% of batters faced (PAs).

This season, when a batter does not swing at pitches just barely outside the strike zone, it is almost three times as likely for the umpire to call it a ball.

In the recent five games (9-13 May), the Diamondbacks batters dramatically turned their walk rate around. In contrast to the league average (that dropped from 9.52% to 9.08%) the Diamondbacks increased their walk rate from 7.63% to 11.89%.

The increased walk rate directly resulted in more runs. Extrapolating those five games to an entire season would be an extra 64.6 runs!

One situation that can greatly impact the game is the 3-2 count. When Diamondbacks batters did not swing their success rate (they got a walk) was very high (88.9% to 100%).

In the last five games, Diamondbacks pitchers dramatically reduced their walk rate (from 8.87% to 6.43%).