Eric Longenhagen

Major League Baseball is once again using the Arizona Fall League as a laboratory for potential rule changes at the major league level. In the past, the AFL has been a proving ground for rule alterations that have made their way to the top level of play, from the pitch timer, to limits on infield shifts, to the ABS challenge system; other initiatives, such as check swing challenges and fully automated balls and strikes, have previously been tested in Arizona but not implemented in the majors. This year, FanGraphs can report that the AFL is piloting new rules restricting defender positioning both on the infield (with the bases empty) and, perhaps more notably, in the outfield. Though MLB implemented restrictions on where infielders can play in 2023, this is the first time the league is piloting guard rails around where outfield defenders can be positioned when a pitch is thrown.

These restrictions first came to my attention during Monday’s game at Salt River Field, where Brendan Gawlowski and I noticed two things. First, Brendan noticed that the two teams’ corner outfielders were positioned both very close to the foul lines and much shallower than contemporary outfielders typically play. Of course, there are situations where a team might want to strategically align their outfielders like this, but for both teams to be doing so regardless of the hitter or game situation struck us as strange. Here is what that looked like on Monday:

Second, I noticed that there were MLB personnel in the ballpark who have been present during past rule change trials and demonstrations. When these rule change tests involve the implementation of new technology, they typically require a cohort of troubleshooters and observers, especially at the onset, and the press box at Salt River Field has been chock full of non-media folks training on ABS and other computer applications that were unfamiliar to me. In a Fall League ballpark that typically only contains about 100 spectators on a given weekday, these folks stick out like a sore thumb.

Thinking a new rule was being piloted, I spoke on background to AFL field personnel, scouts, and sources with Major League Baseball to help understand the specifics of what was being tested. My sources indicated to me that the league’s motivation is to see if further limiting the locations where defenders are allowed to stand will create more base-hit action and have a positive impact on the game’s aesthetics. These new restrictions will apply to play at Salt River Field; a scout source told me that he was at a Rockies’ Arizona Complex League game (which are usually played on the backfields) where the logistics of this were first being tested.

Dark green hash marks have been painted on the outfield grass and at points along the arc where the infield dirt meets the outfield grass. Defenders have to stand within a certain distance of these hash marks when a pitch is thrown. Think of it like tape on the floor on the stage at your high school’s production of Little Shop of Horrors, indicating where the actors should stand to be in their best light.

These restrictions only apply to infielders when the bases are empty, but they apply to outfielders at all times. Below you can see what the defensive alignment looks like from the press box when the fielders are in compliance:

In this alignment, infielders are forced to play “straight up,” while the corner outfielders are closer to the foul lines, and the center fielder is more shallow compared to where we see big league outfielders normally play nowadays.

The Hawkeye system that tracks balls and strikes, as well as the locations of balls in play and players’ on-field locations, is being used to monitor where the defenders are relative to these painted anchor points on the field. Above the stands, hanging just beneath the press box and visible from the field, are LED boards that show the players whether they are in compliance with the location restrictions. Here was the outfielder board after Monday’s game:

If a player is positioned in compliance with the restriction, there is a green “O” visible as their marker. When they’re in danger of leaving the designated location, it shows an orange line, while a red “X” is visible when they’re no longer in compliance. (Those of you who have done the Pocket Presence drill on Madden will be familiar with this warning system.) I walked onto the field before Tuesday’s game to tease the system and get a sense of how much wiggle room the fielders have. Here is my view from a compliant location in right field:

And here I am moving from the edge of the threshold, to a compliant area:

Penalties for non-compliance are enforced by the field umpires, who can see the LED board from their vantage points. For infielders, non-compliance will only result in a violation if the out-of-place defender is the one who fielded the ball in play; where the runner is placed is then a matter of umpire discretion, though first base seems the most likely spot. In the event a play is made by an outfielder who is outside the allowed radius, how many bases a batter is awarded is again a matter of umpire discretion, similar to the way fan interference is assessed. For instance, if a center fielder is out of position and he robs the batter of a would-be gap double, the umpire can place the batter at second base. As of this writing, I have yet to see a violation called by an umpire, but the Fall League season is still young.

Though my sources would not tell me exactly how much buffer the players have to move around the anchor point — I suspect that’s because it might change as the powers that be decide to tweak it, potentially throughout the Fall League — when I was on the field, it felt to me like three strides on either side of the painted hash mark was the margin for error. My sources did indicate that the latitude the center fielder has is more substantial than it is for the corner outfielders.

This is an experiment in its earliest stages. The sense I got from talking to a league source is that it’s a proof of concept to determine if it’s something worth testing more broadly, not something that’s going to be rushed to the highest levels of play in short order. Still, the broader motivations here are easy to understand. Eliminating infield shifts hasn’t had the desired effect on the rate at which balls in play fall in for hits. Historically, the league-wide batting average on balls in play had hovered around .300, but since 2020, that number has shifted down to about .290 or so (it was .290 in 2026). As Russell Carleton has noted for Baseball Prospectus, the combination of lift-obsessed hitters and teams’ ability to use ball-in-play data to strategically position their outfielders, especially moving them deeper to limit the number of extra-base hits they surrender, has resulted in the BABIP environment we’re currently experiencing.

As I write this, I am watching my second game with these restrictions, and I’ve noticed a few things. Bloop hits are tougher to come by, whereas well-hit balls in play have a better chance of getting over the outfielders’ heads. There are slices over the heads of corner outfielders that force them to flip their hips and change direction along with the ball in play, which is usually only a thing you see the center fielder forced to do. And the corner outfielders are positioned closer to the foul line, which means they have a shot to cut off sharply-hit grounders that would otherwise trickle into the corner, and hold the batter to a single.

Of course, it’s early, and I think we’d do well to wait and compare the ball-in-play and singles/doubles data from Salt River Field (which tends to be publicly available) to the rest of the Fall League (or even regular season MLB exit velo/field vector data) when this year’s slate is done before reaching any conclusions. But across 18 innings of baseball, I’m digging this.