If I introduced you to a team that is first in the NL in ISO, second in slugging percentage and wRC+, third in runs and walk rate, you may be inclined to think they are pretty good. FanGraphs has them listed with a .332 wOBA, good for 3rd in the league. What if that team had the most home runs in the National League? Their pitching staff is in the middle of the pack for ERA and BABIP, and they have the highest ground ball rate. A slightly-above-average pitching staff matched with a lightning offense sounds like a recipe for success. Except this is the St. Louis Cardinals, and they are hanging onto the second NL Wild Card spot with their fingernails.
For those who watch the Cardinals every day, their most glaring offensive deficiency is baserunning. The home runs are there and the OBP is there. But as their GM John Mozeliak said, "When you keep running into outs, that's dumb." Sticking with FanGraphs baserunning stats, the Cardinals are almost always at the bottom.
First, I took a look at FanGraphs' BsR statistic. It aggregates baserunning events to determine how much above or below league-adjusted average a team performs. As a team, the Cardinals are at -12.8. They have cost themselves almost thirteen runs on the bases. The three players who appeared in over 100 games this season (Stephen Piscotty, Yadier Molina, and Matt Holliday) have the worst BsR scores. The Cardinals' BsR leader is Randal Grichuk, who has spent considerable time in AAA this season. Kolten Wong and Tommy Pham (#4 and #5) are predominantly bench players. The Cardinals only have five of fourteen qualifying players with positive scores, indicative of how poor their running game really is.
The chart above shows the Cardinals with the five most plate appearances have the five worst BsR scores. They put their worst baserunners out there most of the time. Every player with a positive BsR score has fewer than 350 plate appearances.
I think the best stat to illustrate this point is UBR. It takes into account tagging up on flyouts, trail runners advancing on a play, taking an extra base, and similar events. This means not only whether a runner takes the opportunity, but the rate of success if he does. UBR uses linear weights, so negative scores mean below average. The Cardinals aren't just last in the National League, they are almost twice as bad as the next-worst team. The Pittsburgh Pirates come in at -6.2 whereas the Cardinals have an UBR score of -11.9.
FanGraphs also tracks the number of runs a player adds to their team based on the amount of stolen bases (wSB). The Cardinals are also last in this category. As a team, they do not steal often: The Cardinals' stolen base leader is Stephen Piscotty with six. Their team wSB score is -4.9. They are 18-19 in one-run games; some of those 4.9 runs lost on the base paths might have been helpful toward getting that ratio above .500.
It is not all bad for the Cardinals. The third (kind of) baserunning component FanGraphs tracks is wGDP. It basically tracks a player's ability to avoid a double play. As a team, the Cardinals have a positive score of 4.0, behind only the Cubs (7.0) and Nationals (4.7) in the NL. While they don't advance or steal, they also don't concede the out on a double play.
As much as I would like an end-all answer to all the base-running mistakes, I don't think there is one. Can they afford to stop being aggressive? Maybe not. The Cardinals can't make themselves faster, so they need to be smarter. They don't steal or take the extra base often, indicated by the low wSB and UBR scores. There are opportunities in favourable situations and they haven't taken those chances.
However, with Matt Holliday on the DL, he is replaced by either Jeremy Hazelbaker or Tommy Pham who represent at least a 2.0 increase in BsR. Aledmys Diaz is also on the DL and his replacement, Greg Garcia, represents at least a 2.5 increase. With BsR leader Randal Grichuk as the mainstay in center field, perhaps improvement will occur by getting more appearances for better baserunners.