The League’s Continuing March Towards Three Outcome Baseball

Writing about baseball in April can be difficult. Things are happening, and the natural inclination is to want to talk about those things, but for most players, we’re talking about 20 or 30 plate appearances. A bunch of starters have pitched one game. Besides changes in velocity, there’s not much we can say about what has happened so far. The Diamondbacks and Twins are the best two teams in baseball right now, so yeah, it’s early.

But while samples are still tiny for players and teams, things tend to stabilize pretty quickly at the league level. And, not surprisingly, the first week of the season was filled with the two things MLB games are becoming known for; strikeouts and home runs.

Through the first week of the 2017 season, the league strikeout rate is 21.9%, almost a full point higher than the record-high 21.1% mark that the league established last year, breaking the previous year’s record of 20.4%, which broke the record previously set in 2013, which broke 2012’s record, and so on and so forth. Setting the all-time league wide strikeout record is just something baseball does every year now.

The increase in strikeout rates drove offense through the floor. But then, in the second half of 2015, home run rate took off, and the long-ball trend hasn’t slowed down since. Despite playing in mostly cold weather in the early part of the year, the league wide home run rate so far this year is almost a match for the 2016 home run rate. Generally, home run rates increase as the season goes on, with warmer weather helping the ball carry further, and lower-quality pitchers getting called up to replace guys who got hurt earlier in the year. The fact that we’re starting 2017 near the 2016 seasonal home run rate suggests that this trend isn’t going away.

And as Ben Lindbergh wrote before the season started, this is exactly what we should have expected.

Spring strikeout percentage has an extremely strong relationship with regular-season strikeout percentage, boasting a .98 correlation from 2006–16, the years for which spring stats are available via MLB.com. (A correlation of 1 would indicate a perfect positive relationship in which the two stats move in tandem.) And despite some tenuous signs that the called strike zone’s dimensions could be contracting this spring after its years-long expansion stalled last season, the strikeout rate still seems to be rising. This year’s 20.2 percent?—?an increase of 0.8 percentage points relative to last March?—?is the highest spring mark in our 12-season sample.

Over the last 11 campaigns, the regular-season strikeout rate has been 1.4 percentage points higher than the spring rate on average, maybe because the pitchers catch up to the hitters as the season wears on. If we add that typical margin to this spring’s rate, we get an expected regular-season figure of 21.7 percent, which would yield about 1,000 more strikeouts than we saw last season. That result could only strengthen commissioner Rob Manfred’s desire to formally raise the strike zone’s lower bound from beneath the kneecap to the top of the kneecap in 2018. (As that use of anatomy indicates, the strike zone is super precise.)

…

Over the last decade, the relationship between spring and regular-season home run rate on contact has been weaker than that of spring and regular-season strikeout rate, but still strong overall (.73 correlation). Last spring’s rate was the highest on record, and sure enough, it augured a record-setting regular season. As Opening Day approaches, this spring’s rate has reached another new high, which suggests that whatever’s happened with homers since the second half of 2015 hasn’t run its course yet.

Strikeouts have been trending up for a long time; home runs trending up more recently, but in a very noticeable way. Both of those trends continued in spring training, and they continued in the first week of the regular season.

There has been one area where, through week one, things don’t look like the last few years, though, and that’s walk rate. So far this year, the league average BB% is 9.3%, up over the 8.2% BB% MLB put up last year, and way up over the 7.7% mark we saw in 2015. Of course, we’re dealing with 7,000 plate appearances in 2017 versus over 180,000 in each of the last few years, but through the handy splits leaderboard, we can actually compare weekly walk rates over the last few seasons.

Going back to 2014, so we have three full years of data plus the first week of 2017, no week with a full slate of games has seen a higher BB% than the first week of the 2017 season.

Weeks with a league-wide walk rate over 9% haven’t just randomly happened. The last time we saw a weekly walk rate over 9% before last August was May 9 to May 15 of 2011, when the league wide BB% hit 9.2%. In other words, we’d gone over five years without a weekly walk rate over 9% before last August, but now it’s happened twice in the last six weeks of the MLB regular season.

As Jon Rogele noted in his piece on the 2016 strike zone, the strike zone appeared to slightly contract last year after several years of significant growth, and Jeff pointed out that in spring training this year, we saw fewer low called strikes than in prior years. And with an unusual spike in the first-week walk rate, it may be possible that the strike zone is going to shrink again this year, even without the MLBPA’s agreement to change the rulebook definition of where the bottom of the zone begins.

But because the caliber of stuff of Major League pitchers just continues to get better, increasing the walk rate may just offset the rise in strikeouts to some degree. Because right now, it looks like MLB hitters just can’t hit strikes from MLB pitchers with anything close to the same regularity as they did 10 years ago.

In 2008, the first full year of PITCHF/x data, the league rate on contact in the strike zone (Z-Contact%) was 88%. It basically stayed there for four years, until it dropped to 87.3% in 2012, and then it hung out close to that mark for the next four years.

Last year, in-zone contact fell to 86.5%, and after a one-year pause, the league strikeout rate shot up again. The league’s in-zone contact rate through the first week of this year? 85.3%. Because the best pitchers are the only ones who have made two starts thus far, these numbers aren’t an apples-to-apples comparison to full year numbers from prior years, and this will likely go up once the number of innings is more regularly distributed between pitchers, but the early data suggests we’re in for another year well below the established Z-Contact% norms we got used to over the last decade.

Which makes sense, given that every team now has six or seven guys throwing 95 with knockout breaking balls in their bullpen, and that it’s not even that weird that we have starting pitchers sitting 97 or 98 for extended outings these days. It’s just harder to hit pitches that go this fast and move this much, and even if the league is moving to take away the expanded strike zone that pitchers have enjoyed in recent years, offense will only increase if hitters can hit strikes.

In week one, they didn’t, so league wOBA was still just .316 even as the ball continued to fly out of the ballpark.

It’s just one week, and things can obviously change. Perhaps the league walk rate will sink right back to to closer to 8% this week, and this will all look like nothing but small sample size theatre. But given what we already knew about how the game was changing heading into the year, the strikeout and home run trends aren’t surprising, and the league has made it clear that it would like a smaller strike zone, so perhaps the jump in walk rate shouldn’t be surprising either.

But if you were looking for reason to think the move towards three true outcomes might slow down, well, the first week of 2017 offers basically no hope for you. Unless the first week spike in walk rate was a fluke, we may very well be headed for a record low number of balls in play this year.