After years of mostly sluggish defense and station to station baserunning, the Tigers have made a strong effort to improve their team speed and athleticism. Since 2013, they have added shortstop Jose Iglesias, second baseman Ian Kinsler, and outfielders Yoenis Cespedes, Rajai Davis and Anthony Gose. The changes have helped them go from near the bottom the American League defensively in 2013 (-66 Defensive Runs Saved) and 2014 (-65) to above average in 2015 (+11). The added speed has not, however, translated into success on the bases.
At first glance, it may appear that the Tigers are a good baserunning team. After all, they do lead the American League with 44 stolen bases including 12 for Davis and 8 for Gose. However, they also lead the league with 20 caught stealing and their resulting 69% stolen base percentage is only league average. What does this mean in terms of runs? The wSB statistic at FanGraphs estimates that they have gained only a fraction of a run (0.2) compared to an average team through base stealing.
The more obvious event which is causing the Tigers to make outs on the bases in grounding into double plays. They lead the American League with 54 GIDPs, 10 more than the Red Sox who are the next closest team. The wGDP measure estimates that the Tigers have cost themselves a league-worst 4.2 runs on double plays.
Grounding into double plays is not all base running of course, but you would think a speedy team would be able to avoid double plays better than a slow team. First baseman Miguel Cabrera (8), catcher James McCann (7) and third baseman Nick Castellanos (7) have hit into the most double plays but speedsters like Cespedes (6) and Iglesias (4) have not been immune.
Other base running events include taking extra bases on hits, advancing on ground balls and fly balls and avoiding pickoffs and other outs on the bases. Numbers at Baseball-Reference, Baseball Prospectus and FanGraphs suggest that the Tigers have not been particularly good at any of those things. The UBR measure at FanGraphs estimates that the Tigers have cost themselves 2.7 runs on the bases beyond stolen bases attempts and double plays.
Summing all the numbers - wSB, wGDP, UBR - the Tigers are an estimated 7 runs below average (BsR=-6.7) which places them ahead of only the White Sox (-12.1). The Tigers best baserunners according to this number are Kinsler (2.2) and Davis (1.3). The worst are Castellanos (-3.7) and Victor Martinez (-2.3).
There is no doubt the Tigers have more speed on the team than they have had in a while. This is helping them defensively, but not offensively. We can guess that they are being over aggressive or just not very smart on the bases. As you can tell from the magnitude of the numbers, it's not a huge problem. Sub-par base running hurts a team less than poor hitting or fielding. It's an area where they should be doing better though and it's something to watch in coming weeks.