BP Unfiltered: ERA, Falling Slowly

On Tuesday against Houston, Jarrod Parker pitched seven innings of one-run ball. After a rough start to the season, Parker has lowered his ERA to 3.79. Cory Schwartz of MLB.com noted an interesting fact about Parker’s last 15 starts:

Jarrod Parker has now lowered his ERA in 15 straight starts, the longest streak since at least 1998. Can anyone find the last longer streak?

— Cory Schwartz (@schwartzstops) July 24, 2013

A good research problem for the Fun Fact Department. I dived into BP’s database and found out just how rare Parker’s feat is:

Relief appearances, if any, are excluded.

Since 1970, Mike Morgan is the only pitcher to have lowered his ERA in more than 15 consecutive starts. Morgan, then in his first season of a four-year contract with the Cubs, opened the year allowing six runs in five innings (a 10.80 game ERA), and pitched well enough to lower his ERA down to 2.66 by his 18th start.

It takes some bad starts early on, plus a good four months of consistency, to build such a streak. Parker’s next two starts come against the Angels and Rangers, where the Athletics hope he’ll pitch well enough to extend his streak and their division lead.

Update: Per SC’s comment below, I ran my SQL query in the opposite direction. Here are the streaks of consecutive games that increased the starter's ERA in a season (since 1970):

Dan Haren tops this list of all streaks 11 or higher. He posted a 1.58 ERA in his first 14 starts, and it went up (or down?) from there for 18 straight starts.

These stretches end for an assortment of reasons. A few starters were pulled, though they might've returned for a few bad starts, which my query counted. Charlie Leibrandt's streak was the worst of this group, posting a 10.01 ERA over ten starts (plus an 11th, a two-inning, six-run outing). That year, Leibrandt was the number three starter for a 92-win Royals team.