Inside the Key Oakland A's/Seattle Mariners Series

Having to face King Felix and Hisashi Iwakuma in the same series troubles Oakland's .328 OBP.

For the second time this year, the A's have gone 1-0 in a doubleheader. At least that's the way it must feel after winning their second game of 18 or more innings.

The good news is that they swept the Yankees and took the season series with New York 5-1. The bad news is that the series saw Yoenis Cespedes and Coco Crisp sustain leg injuries and miss two games each (these are supposedly minor injuries that the team is wisely handling with caution). And the bullpen just ran through six relievers for ten innings of work in one game.

That's bad news, because the A's are facing a pair of AL nemeses the next week, starting with the Seattle Mariners. Strangely enough, Seattle is the only team in the division with a winning record against Oakland. How have the third place Mariners, mired nine games below .500, stuck it to the division leaders by taking four of seven so far? Superb pitching mixed with a little bit of luck.

Low OBP and Unlucky Pitching Matchups

Oakland's on base percentage of .328 has been a key reason for the team's success. It's the fourth best percentage in the AL, largely due to the fact that the A's walk in 10.1 percent of all plate appearances, the best percentage in the league. That's helped the club score 4.65 runs per game, above the AL average of 4.39.

However, against Seattle, Oakland's offense has been anything but above average. The team has scored only 23 runs in seven contests (3.3 R/game). The A's on base percentage against Seattle is the worst the team has against any opponent at .262. Key in the club's struggles to get on base against the Mariners is a plummeting walk rate in those games (5.9 percent).

The A's have also been unfortunate in their draw of pitchers, and this is where the tiny bit of good fortune for Seattle comes into play. After this upcoming series, Oakland will have faced Seattle's two best pitchers - Felix Hernandez and Hisashi Iwakuma - five times in ten games. It's not terribly uncommon to have faced two starters in half of their matchups, but it is terribly unfortunate for the A's.

The disparity between the Mariners top two guys and the bottom three is astounding. Iwakuma has an ERA of 1.79 in 14 starts. King Felix's is 2.49 in the same number of starts. No other starter has an ERA below 5.12. (except Jeremy Bonderman who only has a three game sample size).

The A's are scoring 1.3 runs per game against Hernandez/Iwakuma and 4.75 against all other Mariner starters. With two of three games this series against the top of the rotation, Oakland will have to work hard to even this series at five games apiece, let alone take a lead.

Compounding the lineup's struggles is the fact that the Mariners' walk rate jumps from a below average mark of 8.1 percent for the season to a superb 11.3 percent against the A's. Their home run rate against the A's is also 3.5 percent compared to 2.8 percent against all other teams.

Improving play against Seattle is particularly important with six of Oakland's next 10 games coming against the Mariners. Throw in a four game set with the Rangers wedged between the two Seattle series, and this is an opportunity for the A's to increase their lead over the second and third place teams in the division, or to allow both to close ground (and in the case of Texas, take first place).

It's a critical stretch of June baseball for Oakland, to say the least.

Matt Keith covers the Oakland A's weekly for numberFire. Contact him at or on Twitter @mattlkeith.