Strand rate is the percentage of batters that reach base but do not score. A typical number is .75. If a pitcher has a STR this season that is extremely different from his career norm, then it's safe to assume a correction in ERA from here on out.
Dan Haren (.86 STR) – I've chronicled Haren's season regarding luck before, but it's truly remarkable how well things have gone his way so far. He leads MLB in BABIP (.225), leads the league in STR by .05 and has decreased his HRs allowed dramatically (.73 HR/9 IP) despite giving up more flyballs this year than in the past (0.82 G/F). The extreme amount of foul territory in Oakland certainly helps, and Haren has been known to add a few extra mph on his fastball with runners on base, but there's no denying how fortunate the young hurler has been. To emphasize this point, Haren's career STR is a below average .70.
Other pitchers who have been able to pitch out of jams at an unsustainable pace include: Brad Penny (.81), John Maine (.81), Chris Young (.80), John Lackey (.80) and Ian Snell (.79).
Note: A quick glance at this list reveals one thing in common – all are good pitchers. However, most of these strand rates deviate from their career norms fairly drastically, so it's pretty easy to see why the majority have ERAs less than 3.0. They are unlikely to finish that way.
On the opposite side of the spectrum, plenty of pitchers have simply been unlucky when the hits have fallen. However, this is a trend for some hurlers, highlighting why impressive peripherals (K:BB ratio) don't always lead to impressive ERAs.
This group includes: Anthony Reyes (.54 STR), David Bush (the 3.71 K:BB ratio is nifty, but the .59 STR is the worst in MLB among starters who have reached the 72-inning minimum), Javier Vazquez (career 3.25 K:BB ratio/.69 STR. It's .65 this season). These guys cannot pitch out of the stretch and are especially vulnerable to the big inning. I'd avoid them moving forward.
As for the unlucky group, it starts with Roy Halladay, whose .67 STR is well below his career mark of .73. Expect improvement in Halladay's ERA from here on out. Others include Jose Contreras (.66), Bronson Arroyo (.66 – although there's injury concern here), Ted Lilly (.67) and Daniel Cabrera (.67).