During the 2012 offseason, the Mariners added several aging/broken/sluggish sluggers (i.e., Michael Morse, Raul Ibanez, and Kendrys Morales) to their roster in an effort to put together a team that would be able to hit lots and lots of dingers. Unfortunately, the relatively blobby physiques and not-so-fleet feet of these men enabled them to do little else. As a result, the Mariners ended up with a franchise low 49 stolen bases in 2013. (I guess they did have just 48 SB in 1994, but they also only played 112 games in 1994.) Their second lowest season-long total was 81 (reached twice, in 1989 and 2007), so 49 SB broke the record by a lot.
Fast-forward to this year. In 2014, the M's stole 96 bases. That's almost twice as many! They must've really improved in terms of their base running, right? Maybe. Looking at stolen bases alone isn't really sufficient to determine how valuable a team's base running skills are. To get a more realistic interpretation, it's also necessary to consider other variables.
Fangraph's does this using their base running (BsR) stat, which is a combination of a team's/player's weighted stolen base (wSB) runs and their ultimate base running (UBR) runs. These may be statistics that folks are a little less familiar with, so I encourage you to click on those links if you're at all fuzzy about these concepts. Simply put, UBR looks at how much value a player contributes in terms of going first-to-third on a base hit, tagging up on fly balls, moving up on groundouts, etc., while wSB looks at how successful a player is at adding value via the stolen base. (I should note that single-season BsR is more of a descriptive stat than it is a predictive stat. If you want to predict future BsR values, you need to analyze the data from more than one season.)
It's interesting to note that although there is some correlation between a high UBR value and a high wSB value, this relationship is not as strong as it could be. Here's a look at the 146 qualified batters from 2014 and how they fared on the basepaths.
Looking at this plot, we can see that some players are good at all aspects of base running (Ben Revere) while others are only particularly proficient at either stealing bases (Jose Altuve) or advancing on balls in play (Hunter Pence). This suggests that although foot speed is definitely beneficial to all aspects of base running, it's not the only variable that matters. A player's ability to provide value on the basepaths is made up of both intrinsic and learned abilities.
As for the M's, here are the UBR vs. wSB values for Seattle batters with more than 100 PA in 2014:
James Jones is FAST. This enabled him to be an excellent base-stealer last season. His wSB of 4.7 was the fifth highest in all of baseball! However, he actually had a negative UBR value. As a rookie, maybe this isn't entirely unexpected; there are a lot of little things a player has to learn, in terms of both mechanics and reading the ball off the bat/understanding the positioning of infielders/outfielders, in order to move around the bases with maximum efficiency. Speed isn't everything. However, the fact that every other player in the top-20 wSB had a positive UBR suggests that Jones has a good chance to mature into a more complete baserunner as he moves forward in his career.
Alternatively, players like Cano and Ackley (who don't have rocket boosters installed in their stirrup socks) appear to be able to add value by intelligently/quickly analyzing how/where a ball is hit and moving around the bases according. They seem to do more to maximize the speed that they have.
In order to see how the Mariners performed on the bases in 2014, relative to previous years, I've compiled the UBR, wSB, and BsR values from the last 13 seasons (since the inception of UBR):
*The numbers next to the BsR values indicate where the M's ranked among the 30 MLB teams each season.
In 2014, the Mariners improved by more than seven runs in terms of their BsR (from -11.2 to -3.8). This is certainly a step in the right direction, but it's still not good (league average base running values are zero). Since 2002, we can see that the M's have only managed to put up positive BsR values four times and have only cracked the top-12 once. The reasons for these meager numbers are likely related to a combination of several different variables. Some of it may be caused by questionable calls made by base coaches, some of it is caused by bone-headed decisions made by M's players, and some of it may even be due to various park effects. However, the most significant cause is probably related to roster construction.
Recent Mariners teams haven't really been built with a focus on "plus" base running. For the past 10+ years, they've consistently ranked in the bottom third in terms of BsR, to the degree that we've become more or less used to it. As this team moves forward and (hopefully) begins to regularly challenge for a playoff spot, it'll be interesting to see if/how their approach changes.
According to Fangraph's, the difference in BsR runs between the best (Nationals with 12.8 BsR) and worst (Cardinals with -10.8 BsR) base running teams in 2014 wasn't terribly large (less than 24 runs). Compared to the spread in batting runs (~190 runs), this number might seem fairly small. However, it is important to remember that every nine or ten runs above/below average is equivalent to ~one win. A difference of 24 base running runs is significant; after the Mariners performance in 2014, it's very easy to appreciate the value of a single win.