One of the great things about baseball is that it's always changing. The changes don't happen quickly in most cases, but the game being played today is quite a bit different from the one played 10 years ago, and the one 10 years before that, and the one 10 years before that. Baseball has eras during which no one could hit and eras during which even a shortstop could launch 20 homers a year; it has had eras when starters pitched nearly every inning and eras when a manager would bring in his specialist to counter the other team's newly-inserted specialist.

The current era is all about pitching, as the rise of hard-throwers on every roster and an expanding strike zone have made this a great time to throw the ball for a living -- as long as you can manage to keep from visiting Dr. Andrews, anyway -- and a rough time to try to put up big offensive numbers. This is a drastic change from the style of play that we saw during the Steroid Era, where players used copious amounts of PEDs and offensive rates neared all-time highs. If you've been watching baseball since we entered the 21st century, you've seen the game change in pretty dramatic ways, even while it is still the same sport.

Over the last 50 years, one of the most interesting changes has been the rise and fall of the popularity of the stolen base. Aggressive baserunning reached its peak in the 1980s, when teams like the St. Louis Cardinals featured lineups of slap hitters who could run and field, while stars like Rickey Henderson and Tim Raines were also setting the standard for what leadoff hitters should be. But when home run rates surged in the 1990s, stolen bases were de-emphasized; why risk making an out when the next guy up can hit one over the fence?

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Now, with the strike zone getting bigger and PED testing getting more sophisticated, offense is back to the levels we saw back in the 1980s, with teams averaging roughly 4.25 runs per game over the past five years. With runs being scarcer, it was thought that perhaps MLB would move back toward 1980s-style players, and we'd see a resurgence in stolen bases.

That happened, sort of. To illustrate the long-term and recent trends, here is a graph of the rate of stolen base attempts (SB+CS) per plate appearance over the past 50 years in MLB:

You can see the big spike from 1976 through 1990, with the league averaging approximately three stolen bases for every 100 plate appearances during that stretch. The Steroid Era chased speedsters out of the game, so the rate regressed back down to 2 percent in 2003 and hovered around there through 2008. The game was evolving at this point, with plenty of holdover stars from the age when offense was plentiful, and it's not like MLB teams can so easily just swap out players for a different approach whenever they feel like it. Changes take time, and when stolen base rates started climbing from 2009 through 2012, it looked like perhaps MLB teams were indeed reacting to the new normal of lower offensive levels, putting more speed-and-defense athletes on the field.

Except that trend reversed course quickly in 2013. And this year, stolen base rates per plate appearance rates have returned to the 2 percent floor that we saw before the speed explosion of the 1970s and 1980s. Of course, some of that is just a function of opportunity; it's hard to steal a base when you've just struck out, and as we know, strikeouts are at an all-time high. While low-offense eras should promote risk-taking strategies like stealing bases, you have to get on base in order to attempt a steal, so perhaps SB/PA isn't the right metric to illustrate team aggressiveness.

To make sure we're not measuring the wrong thing, let's look at stolen bases relative to the number of singles, walks and hit batters for each of the past 50 years. Certainly, not every single/walk/hit batsman results in a stolen base opportunity and there are stolen base opportunities that occur after events other than those, but the number of reached-first-safely plays should serve as a decent proxy for stolen base opportunities over the years. So, here's that graph:

The trend-line is the same shape, as we'd expect, but there are some subtle differences here. If you look at the tails, you'll note that, unlike the SB/PA graph above, we're actually not quite back to the rock-bottom stolen base attempt rates of the early '€˜70s; the uptick in strikeouts is masking things a bit, as there are just fewer chances for players to steal than there were in prior low-offense years. But even adjusting for that, we're definitely still at a relative low point in stolen base attempts despite the scarcity of offense.

So, what's the deal? Why are major-league teams still playing station-to-station baseball even though three or four runs wins you a game these days?

Well, it might actually have something to do with those strikeout and home run trends we've mentioned. While it's still happening somewhat under the radar -- since overall offensive levels are still down -- home runs have come roaring back in baseball this year, to the point where the rate of home runs on contacted balls is the same now as it was a decade ago. We're not seeing guys hit 50 or 60 home runs anymore, but that's mostly because guys don't hit the ball as often as they used to, not because it isn't going as far when they do hit it.

This year, 23 percent of all plate appearances are ending in either a strikeout or a home run, the highest total on record in league history. The base you're standing on is entirely irrelevant if an at-bat ends in a strikeout or a home run, so with those two both trending upward, the potential reward for stealing a base is not as high as one might think based on the level of offense in the sport right now. Back in the 1970s and 1980s, when only about 15 percent of all plate appearances ended in strikeouts or home runs, stealing a base had a much better chance of being followed by an event where the stolen base could matter. So not surprisingly, teams ran more then.

There's some evidence that teams probably ran too much back then, actually, and all those base-stealing attempts were inefficient, given how many outs teams were giving away in the process of trying to advance their runners. And in this modern era of data analysis, teams certainly are more wary of giving away outs than they used to be. So, unfortunately for those of us who like watching athletes run and catchers throw, it looks like we probably aren't headed back toward dramatically higher stolen base rates any time soon. Even with diminished run-scoring abilities, the current norm in baseball is to still stand around and wait for the three-run homer; the only difference now is that we usually get the inning-ending strikeout instead.