By almost every measure, the Detroit Tigers have the worst overall pitching staff in the American League in 2015. In fact, the Tigers arguably have the worst starting rotation, as well as the worst bullpen in the league as presently constructed.
The Tigers' pitching staff has an fWAR of just 5.9, which is dead last in the AL this season. Detroit posted a team pitching WAR of 17.7 in 2014, and led the league with 26.8 WAR in 2013. David Price accounts for 3.6 WAR by himself, over half the team's total, leaving the rest of the team with less than half the WAR of the second-worst team in the league.
The Tigers also have the highest team ERA at 4.77, and the highest FIP at 4.47. Their combined home run ratio is 1.23 HR per nine innings, which is also by far the highest in the league. Any single pitcher with a ratio that high would be a cause for concern, but for the team as a whole, it's more like an epidemic.
The Tigers rotation, which was historically good as recently as 2013, now has the highest ERA and its bullpen has a combined ERA of 4.75, also highest in the AL this season. The bullpen also has an fWAR below replacement level for the second season in a row, at -0.4.
With the loss of Max Scherzer to free agency, the trades of Rick Porcello and Drew Smyly over the past year, and injuries to Justin Verlander and Anibal Sanchez, one could certainly expect a decline in performance from the starting rotation.
David Price adequately replaced Scherzer for the first four months of the 2015 season, but when Price was traded in July for prospects, Detroit had officially gone from first to worst in pitching, despite a much improved defense this year. The Tigers' rotation without Price is even worse than the Tigers' bullpen, and that is saying something.
The Tigers are allowing 5.05 runs per game so far this season. That would put them on pace for 819 runs allowed by the end of the season, and they've picked up that pace considerably in recent weeks. Last year's team allowed 705 runs, and they have already given up more runs than they did for the entire season in 2012 or 2013.
That run total would be more than they have allowed since 2008, when the team surrendered 857 runs. As the team looks to regain their status as contenders in the AL, the primary focus will have to be on improving the pitching staff across the board.