The Mariners rotation has provided the team with a lot of long outings this year. You can slice and dice the numbers many ways to cherry pick results to show different peaks of starter endurance. For instance, the Mariners lead the league in percentages of starts that last at least 6.1 and 6.2 innings. However, they're only 14th in percentage of starts that last at least 6.0 innings, which is a hilariously large discrepancy.
Perhaps the two simplest measures of starting length, mean and median, both yield good results. By average, a Mariner start in 2010 has lasted 6.1 innings, eighth best in the league. Their median is even better thanks to Ryan Rowland-Smith's constantly short outings. At 6.2 innings, only Tampa and San Francisco can even match the Mariners.
A big reason for those long outings? Good control. Mariner starters average 1.7 walks per outing and just an overall 7% walk rate, good for seventh best in MLB and second best in the AL behind the ever-strike-throwing Minnesota Twins. The M's might have better control though as among pitches recorded by Pitch F/X, the Mariners actually come out tops in the league for locating pitches in what I define as the strike zone at a robust 46%.
Thanks to that walk avoidance, the Mariner starters have also been efficient in getting through their innings. Despite averaging the eighth-longest outing, they throw just 98 pitches on average per start, fifteenth in baseball. They have been eating innings without eating up tissue in their shoulders or elbows.
Even with missing a month of Cliff Lee and the implodey starts of Hyphen, Ian Snell and a few mess ups from Felix Hernandez, this rotation has consistently kept our bullpen rested. In fact from April 12th through April 30th, the Mariner rotation made 16 consecutive starts of at least five innings. Jason Vargas' shortest outing was yesterday's five inning stint. After Doug Fister's first start of the year, he's gone at least five in every attempt.
Only once all season has there been back to back starts of shorter than five innings. Even that was not much of a strain as it was preceded by a string of starts that went 8.0, 6.2 and 8.0 innings and was immediately followed by a string of starts going 7.0, 7.1 and 7.1 innings.
For as long as this keeps going, there is absolutely no reason for this team to even think about carrying a seventh reliever.