What happens if baseball changes the strike zone?

It sounds like such a small change, what the Commissioner proposed the other day. But moving the strike zone slightly up from the bottom to the knee to the top could have profound implications not only for how the game is played, but how we think about how rosters are constructed.

There's no doubt that we're in a period of profound offensive slumpitude, especially in comparison to baseball ten years ago. As recently as 2006, clubs were scoring an average of almost 4.9 runs per game, but we've seen that greatly reduced to just around 4.25 runs per game. To put that in some context, there were almost 3,000 fewer runs scored in baseball in 2015 than there were in 2006. The difference is even starker if we go back to the turn of the century (God, that's an amazing phrase to be able to write).

Part of the reason for that change is that umpires began calling the low strike according to the rule book. Some of that is probably because of the introduction of Pitch F/X and Major League Baseball's decision to start holding umps responsible for the strike zones they call. And there's no doubt that a larger strike zone inherently helps pitchers, forcing batters to chase after balls they normally wouldn't.

Again, it sounds like a small change, but the results could be quite profound. For one thing, pitchers who work low in the zone will be disproportionately affected by the change. Just a few days ago, Eno Sarris identified Zach Britton's sinker as the most effective pitch in baseball (behind a paywall, sorry). Jeff Sullivan also found a bunch of similar pitchers, including dynamic young starters Aaron Sanchez, Carlos Carrasco, and Carlos Martinez, who generate a ton of value through their sinkers. Taking away, or at least reducing the frequency of, that low strike is going to be death for these guys, along with all the others on this list FanGraphs published earlier today. Hitters will simply lay off their sinkers, forcing them to throw the ball further up in the zone.

And the further toward the middle of the strike zone pitchers move, the harder and further baseballs are going to get hit. Indeed, there is a dramatic rise in slugging percentage per pitch in the lower half of the zone as pitches rise, according to the Pitch F/X heat maps on Fangraphs. The end result is that we will see a rise in offensive levels across the games. Home runs will go up, and so will walks. Strikeouts will fall.

I generally have a lot of confidence in most front offices understanding these dynamics, and adjusting accordingly. But it takes us fans, and writers, a few years before we catch up to changes in context. By the time we do, baseball is generally on to other things. Indeed, just now, we're starting to become reaccustomed to ERAs in the high threes being average. Mark Buehrle had a 3.81 ERA for his career, which was 16 percent better than the league average. But his 3.81 ERA in 2015 was only four percent better. In 2006, Brett Anderson's 3.65 ERA would have been in the top 20 in all of baseball. Today, it's essentially average given his ballpark and league, and he wisely took the Dodgers' qualifying offer rather than risk going on the open market. Buehrle just up and retired.

Tomorrow, those marks are likely going to be excellent and our expectations are going to have to change all over again. Mediocrity is a moving target, just as is, apparently, the strike zone.