1) Miguel Cabrera (and his health)
This one is really no secret, as anyone that has watched Cabrera play knows that he's not going at full speed, and can't produce at the level he did for much of the year. The numbers help paint the picture of just how much it was really impacted though.
For the year, Cabrera created 144 runs (based on wRC), good for the most runs created in baseball. However, that glosses over the stark contrast of Miguel's season. Over the first five months, he averaged creating almost 27 runs each month, or a little over one run per game. In September? Just 10.5 runs runs created in the 20 games he played, less than half his production for the first 128 games of the season.
Had Cabrera been healthy, it would have been safe to tack on another 10-15 runs to the Tigers run total for the month, and it would have moved the Tigers up to about 4.2 runs/game, or about 15th in MLB. In other words, Cabrera is a big chunk of the Tigers offensive draught, but he is by no means all of it.
2) The Power Outage
Again, the offense saw plenty of power through the first five months, averaging 32 home runs in a month. But in September, that month was cut in half, to just 16 home runs. Again, some of this is Cabrera, but even at his peak, he wasn't hitting 16 home runs in a month (the most was 12 in May of this year), so there are other culprits.
Surprisingly, despite having a rough year, Prince Fielder produced exactly as expected. He posted 25 home runs for the year, or about four per month, and his September total was just that; four.
Instead, just about every member of the everyday lineup saw some of their power sapped in the month. Omar Infante, Andy Dirks, Austin Jackson, and Torii Hunter hit just one home run apiece. The Tigers overall home run per fly ball rate fell to 7.0%, after being over 11% through the first five months. In addition, while their line drive rate held steady, they saw a skew in their ground balls/fly balls – fewer balls in the air, at just 31%, compared to 34% coming into the month.
Suffice it to say, the Tigers weren't getting under balls in September like they were in much of 2013, and even when they did, they didn't have the legs to reach the fences (some of this could certainly be unfortunate luck or circumstance, but could also be indicative of injuries or players tiring).
How many runs come from a home run can be up for debate – strictly speaking, it's one run each time, guaranteed. Of course, that overlooks runners on base that could have also scored. At an estimated 1.4 runs per home run, had the Tigers gotten half the total they missed from their monthly average (factoring out Cabrera), an additional 8 home runs would have produced 11 more runs, boosting the Tigers to 118 runs, which would have been good for 8th in MLB in September.
3) OBP Suffers, Especially at the Top of the Order
The Tigers were never the most patient team in baseball, but still posted a .346 on base percentage for the season with an 8.3% walk/plate appearance – through August, it was 8.6%.
In September, those numbers limped in at .323 with a 6.7% walk/plate appearance. The same walk rate would have produced about 19 additional walks, or about an additional seven runs. These walks also would a multiplier effect, as a walk means another plate appearance by which someone could get another hit, walk, etc. Adding on seven more runs (even though it's probably more), the Tigers are up to 7th in MLB in runs scored in September.
This walk rate lacking was especially felt at the top of the order, where Hunter and Jackson each posted an OBP around just .300 (Jackson at .307, Hunter at .295). If the guys at the top of the order can't get on base, the middle of the order can't drive them in with the same regularity, either.
What Does It All Mean
It means, for whatever reason, the Tigers are slumping at the plate when it matters most.
In one case, Cabrera, there's simply not much that can be done. A season's worth of nagging but persistent injuries have taken their toll, and while his superb hand eye coordination and bat control will likely keep him hitting .300, the power won't return until after an off-season to heal.
As for the other two factors, the Tigers have already decided to make one move for Monday's game three, inserting Jhonny Peralta in left field, hopefully giving the Tigers some more pop in the lineup. Beyond that, there's not much else they can do about the power – either they all hit a stretch of bad luck at the same time that they need to turn around, or a combination of older players are tiring after a full season of work without much rest and potentially other unmentioned nagging injuries are preventing players from turning on pitches.
Last but not least… the walk rate. The Tigers took no walks in game one, and walked just twice in the second game. In a game with around 35 plate appearances, the Tigers should be averaging three walks. That means more patience at the plate, not swinging at pitches outside the zone, and especially forcing the Athletics' pitchers to beat the Tigers, not the Tigers beating themselves by swinging early in the count at pitcher's pitches when a better one could be coming later.
So, there are some things the Tigers can do to shake out of this slump and start putting some runs back on the board. But there are also some things outside of the team's control, which simply means the pressure will be on the pitching staff for the remainder of the postseason run to keep the opposition in check.