(AP Photo/Ed Zurga)

When they added Jon Lester to the rotation in late July, the Oakland Athletics were the second favorite to win the World Series behind the Detroit Tigers. They still find themselves the second favorite, but this time to the Washington Nationals, with the Los Angeles Angels of Anaheim nipping at their heels.

The Angels enjoy a half-game lead over Oakland after beating the Red Sox, 4-2, on consecutive doubles by Mike Trout and Albert Pujols, making it the first time since May 2011 that the Angels were at the top of the AL West all by themselves. If the A’s want to get back in the race, they are going to need their offense to break out of this funk.

Since the trade deadline, Oakland’s offense is below league average, creating 13 percent fewer runs in August than you would expect over the same number of plate appearances.

Oakland is experiencing a decline across the board. Their weighted on-base percentage, which combines all the different aspects of hitting into one metric, weighting each of them in proportion to their actual run value, has dropped from 0.323 in the first half to 0.293 in August. And they have seen similar declines in batting average and slugging percentage.

Their leadoff hitter, Coco Crisp, has really struggled in August. Over the season’s first half, he had a .387 on-base percentage, with a high point of .426 in June. This month he is at .241 and has walked in just 10.3 percent of his plate appearances while striking out on 13.8 percent of them. This all adds up to creating 64 percent fewer runs than we would expect a league average hitter to create with the same opportunities.

Brandon Moss is struggling as well. After hitting .268 in the first half with .530 slugging he is languishing with a  .188 batting average and .229 slugging in August. His decline is a little bit easier to diagnose: His groundball rate has skyrocketed to 36 percent after averaging 31.5 percent in the first half of the season. More groundballs mean fewer opportunities to safely reach base. He is also hitting flyballs less frequently (47.7 percent in first half vs. 36 percent in August) and one has yet to leave the yard this month.

Fluctuations like these typically correct themselves, but Oakland could already be in too deep a hole to catch the Angels by then or worse, find themselves out of the wild card spot.