Regression, defined as a return to a former or less developed state, is a word thrown around a lot in baseball. When a season is so long – when there are thousands and thousands of data points to collect – there’s no reason for fans and analysts of the game to jump to early-season conclusions about a batter or pitcher, only to see those same players regress to their mean.

Sometimes though, things change. Sometimes a return to former play doesn’t occur because a player developed, hitting the ball well or throwing it with more velocity. Good numbers from a surprising source doesn’t always mean regression is about to occur. Perhaps that player is in store for a good season.

Each week, the plan with this article is to look at a handful of guys who seem to be outdoing themselves. While these players are sure to regress, some are bound to do so more than others. And that’s what I’m looking to figure out.

Drew Stubbs, Colorado Rockies

Let’s talk about what Drew Stubbs has done over the last two weeks, because it’s borderline absurd. The man with a career .143 ISO is hitting to a .306 ISO since Cinco de Mayo. He’s batting .444 when his career average is .243. He’s got a wOBA of freaking .503 over the last two weeks, people. What has Drew Stubbs done with Drew Stubbs?

Obviously the Rockies lineup is hitting everything, and playing at Coors helps. But over this time frame, Stubbs has a .538 batting average on balls in play (highest in the league), and is still striking out on 23.7% of his plate appearances. I’d be more willing to say “hooray” for Drew Stubbs, too, if his batted ball profile during this time looked spectacular, but that’s not the case.

His line-drive rate is high compared to his career averages, but sitting just under 30%, you shouldn’t expect a .444 average. Well, you should never really expect that type of average. He’s essentially converting a lot of his flyballs into line drives, which is great and a potential sign of good things, but to believe he’s this good would be foolish. Not that this will matter much though, as Michael Cuddyer is set to return, making that Rockies’ outfield an even bigger mess.

Jacoby Ellsbury, New York Yankees

On the opposite side of the spectrum, Jacoby Ellsbury’s been struggling. He’s got two hits over his last 25 at-bats, and just a .122 average over the last two weeks. A quick glance at his batted ball profile shows that just 12.10% of his balls in contact are going for line drives over this time, while his flyball rate is a high 42.40%. That’s not good.

Fortunately, Ellsbury started the season well, and still has a line-drive rate of 26.0% on the season, a whole six percentage points higher than his career average. This could be more a result of his over-performance to start the year, as he’s regressing more to his norm. Be aware, however, that his low average and BABIP isn’t due to bad luck – he’s really not been hitting that well.

Bronson Arroyo, Arizona Diamondbacks

Arizona righty Bronson Arroyo hit a rough patch in his third and fourth starts of the year, surrendering nine and five runs respectively to two really bad offenses (Cubs and Mets). Over his last four starts, however, Arroyo has allowed just three earned runs, going at least 6.1 innings with each start. He’s taken an ERA of 9.50 on April 21st, and brought it all the way down to a 4.15 mark today.

He’s been especially dominant over his last three starts, one against San Diego, one versus Milwaukee and the most recent against Washington. During these games, Arroyo’s gone 7.0, 7.1 and 9.0 innings, striking out an average of nearly six batters per outing. He’s not a big strikeout pitcher, with a K/9 rate of 5.83 over the course of his career.

It seems as though Arroyo’s compensating for his slow start, which is good news for Diamondback fans. However, over his last two starts especially, he’s been playing a little over his head. Those two starts have seen a higher than normal K rate, sure, but also a .267 BABIP and 86.7% LOB% - both numbers scream regression. His xFIP, in turn, is a decent but not as inspiring 3.08.

Perhaps one of the biggest numbers to point out is his home run rate, which is zero. Arroyo, who tends to give up the long ball, hasn’t allowed one in four straight outings. Props to him, but be prepared for that to change.